Parasite control products for dogs: how they work, risks and how to make a more informed choice

Parasite control is often discussed in very simple terms: drops, a tablet, a collar, a dewormer or a ‘natural’ product. In reality, parasite control is a very broad concept: some products are intended for parasites that live on the dog, such as ticks and fleas, while others target worms or their larvae inside the body. Their mechanisms of action, duration of effect, persistence in the body or coat, removability, adverse effects and potential impact on other family members can differ greatly.

The most important thing to understand from the start is this: no tick-control product can provide a 100% guarantee that a dog will never pick up a tick or become infected with a tick-borne disease.

Parasite-control guidelines also emphasise that no product is completely effective and that using a tick-control product should be combined with regular tick checks.

So tick control is not only a question of ‘which product works?’

More useful questions are: how does the product work? Where is the active substance after administration? How long does it remain in the body or coat? What is its half-life and what does that actually mean? Can the product be removed if an adverse reaction occurs? What adverse effects are known? Can an individual dog’s characteristics affect how the drug behaves in the body? Does the dog actually need every active ingredient contained in the selected product?

The purpose of this article is not to say that all parasite-control products are bad or that they should not be used. That decision belongs to each owner. Ticks and tick-borne diseases can cause serious health problems, so the real question is the individual dog’s lifestyle and actual level of risk. I personally have chosen the natural route, but that is my personal decision.

FendaF’s aim is to give pet owners more information so that the choice is not based only on convenience, advertising, or interpreting the word ‘protection’ on a product as an absolute guarantee.

Quick comparison: jump straight to the tables

If you want to compare a specific route of administration before reading the full article, jump directly to the relevant table:

Collars: effect, duration and removability  |  adverse effects and family members

Spot-on products: effect, duration and removability  |  adverse effects and family members

Sprays: effect and duration  |  adverse effects and family members

Single-ingredient tablets: effect, duration and half-life  |  adverse effects and special considerations

Combination tablets: what they cover and for how long  |  adverse effects and special considerations

Long-acting injection: effect and pharmacokinetics  |  adverse effects and special considerations

Pharmacokinetics: quick comparison of half-life and accumulation

What are parasite-control products actually trying to control?

Before comparing individual products, it is worth looking briefly at which parasites dogs are actually treated against. ‘Parasite control’ includes both external and internal parasites, but the risk of infection depends on very different factors: the dog’s age, activity, hunting, diet, travel, other animals in the household and even who shares the home with the dog.

Parasite / group	How the dog is exposed	When does the risk actually increase?	Important nuance
Ticks	A tick gets onto the dog from grass, scrub, forest or a garden and then looks for a place to attach to the skin.	The dog regularly moves through long grass, forest, scrub or a tick-heavy garden. The risk is seasonal, but mild winters can extend the season.	A tick-control product reduces risk but cannot provide a 100% guarantee against attachment. A dog can still become infected with a tick-borne disease.
Fleas	Adult fleas live on the animal, but eggs fall into the environment and larvae and pupae develop in carpets, cracks, bedding and other areas of the home.	There is a free-roaming cat in the household, several animals, contact with stray or wild animals, or fleas have already entered the home environment. The cat flea Ctenocephalides felis also parasitises dogs very effectively.	A flea problem is not only ‘a flea on the dog’. An untreated cat or other animal can seed the environment with eggs, and the life cycle can continue indoors year-round. Fleas can also transmit the tapeworm Dipylidium caninum.
Lice	Spread mainly through direct contact or contaminated hair/items. Dog lice are fairly host-specific.	Close contact with infested dogs, shelters, kennels, poor coat care or high animal density.	The risk in an ordinarily well-cared-for household dog is generally lower than for fleas or ticks, but infestation can spread quickly in groups.
Mites	Sarcoptes spreads through contact with an infested dog or wild carnivore; Otodectes ear mites spread between animals. Demodex is different: the problem usually arises when mites already present multiply excessively, rather than through a classic new ‘infection’.	Contact with dogs with sarcoptic mange or foxes, multi-animal households, shelters/kennels; for Demodex, young age or a condition that disrupts immune balance.	Not all ‘mites’ have the same epidemiology, so one universal prevention strategy does not apply to all of them.
Mosquitoes and sand flies	They are mainly vectors of pathogens. Mosquitoes can transmit Dirofilaria spp.; sand flies can transmit Leishmania. Some topical products are also intended to repel these vectors.	Mosquito-heavy environments, outdoor exposure and travel. Sand-fly risk is especially important when travelling to endemic areas.	Dirofilaria is no longer only a theoretical travel risk in Estonia: D. repens is established in the Baltic region and there are documented indications of local D. immitis transmission in Estonia. The prevalence is still unknown.

Internal parasites and parasites that a typical ‘tick treatment’ does not cover

Parasite / group	How the dog becomes infected	When does the risk increase?	Important nuance
Roundworms (Toxocara etc.)	Eggs from contaminated soil and faeces; with Toxocara, also transmission from mother to puppy and via prey animals.	Puppies, hunting or eating rodents, contaminated outdoor areas, frequent exposure to faeces from other animals.	Toxocara occurs throughout Europe and is zoonotic. Risk assessment also depends on whether the household includes a small child or another person more vulnerable to zoonotic infection.
Hookworms and whipworms	Infection occurs from contaminated environments; some hookworms can also penetrate through the skin.	Faecally contaminated soil, kennels or high animal density, travel and regions where the parasite is more common.	Not all species are equally common in Estonia, so faecal testing and lifestyle are often more informative than automatically choosing the broadest possible tablet.
Tapeworm Dipylidium caninum	A dog becomes infected by swallowing an infected flea or, more rarely, a dog louse.	Fleas. If a dog or cat has fleas, Dipylidium infection is also possible.	Deworming alone is not enough if the flea problem remains unresolved.
Taenia and Echinococcus	Infection occurs through eating prey, rodents, raw offal or carcasses.	Hunting dogs, free-roaming dogs, catching rodents, eating raw offal or uninspected organs.	Echinococcus multilocularis occurs in Estonian wildlife. Disease in the dog may be inapparent, but the parasite is important from a zoonotic perspective.
Dirofilaria immitis and D. repens	Larvae are transmitted by mosquito bites.	Mosquito-heavy environments, travel and areas where transmission has been demonstrated. In Estonia, possible local infection has also been described in dogs with no travel history.	A 2024 analysis of Estonian cases indicated local circulation of D. immitis, but those data cannot tell us how common infection is in the Estonian dog population.
Lungworms (e.g. Angiostrongylus vasorum, Crenosoma vulpis)	Infection is associated with snails and slugs, and sometimes with intermediate or paratenic hosts that have eaten them.	The dog eats snails/slugs or encounters them regularly; travel to endemic regions.	A. vasorum has been found in wild carnivores in Estonia. The first molecularly confirmed canine case in Estonia was published in 2026, but the dog had been imported. This does not prove widespread infection in Estonian pet dogs.
Intestinal protozoa (e.g. Giardia, Cystoisospora, Cryptosporidium)	Contaminated water, faeces and environment; transmission is easier where many animals are kept together.	Puppies, kennels, shelters, groups of dogs, contaminated drinking water or recurring gastrointestinal problems.	These are parasites too, but a routine flea/tick product or dewormer may not cover them at all. Diagnosis and separate treatment may be needed.

So the question is not simply whether a dog should receive parasite control. First ask which parasite you are actually trying to control and how likely this particular dog is to be exposed. For example, a free-roaming cat can increase the risk of a household flea cycle, prey-borne tapeworms are more relevant for hunting dogs, and travel changes the importance of entirely different vectors and worms.

In this article we go into the greatest detail on tick and flea products and combination products that include them, because this is where mechanisms of action, persistence in the body, removability and family-member exposure differ especially widely. The internal-parasite section is included so that ‘parasite control’ does not become an inaccurate synonym for ‘tick medicine’.

This does not mean that a dog should automatically receive the broadest possible combination product just to cover every conceivable risk. A combination product is justified when the dog genuinely needs simultaneous treatment or prevention against the different parasite groups covered by its active ingredients. More active ingredients do not automatically mean better parasite control.

Tick control specifically: it is risk management, not a guarantee

A tick-control product may repel a tick, interfere with feeding, or kill the tick after attachment. These mechanisms are not the same.

Repellent products aim to reduce the likelihood that a tick attaches and feeds. With systemically acting products, including many isoxazolines, the tick generally has to attach to the dog and begin feeding before it is exposed to the active substance.

The tick may still die quickly, but the risk of transmission of tick-borne pathogens cannot be eliminated completely.

Pathogens differ, and the time required for transmission is not the same for all of them. That is why tick checks remain important even when a dog is using a parasite-control product.

FendaF has a very concrete example of this. Despite regular spot-on tick control, Peku picked up a tick and developed Lyme disease. The product’s stated duration of action was four weeks, yet the owner applied it every three weeks. Peku’s case cannot tell us how often this happens or how effective the product is overall, but it shows very clearly why tick control cannot be treated as an absolute guarantee against ticks or tick-borne disease. You can read Peku’s longer story in a separate FendaF article.

The risk is seasonal, but tick season should not be judged by the calendar alone. The castor bean tick can be active at temperatures of around +5 °C, and during mild winters ticks may be encountered outside the usual tick season. In autumn and early spring, it therefore makes more sense to watch actual temperatures and weather conditions than to rely only on the month or the first snowfall.

Not all spot-ons and not all tablets work in the same way

The route of administration alone does not tell you how a product behaves in the dog’s body.

For example, two products may both be applied to the skin as spot-ons, but:

• one active substance may remain mainly on the skin and coat;
• another may be absorbed systemically through the skin.

The same applies to active substances.

For example, Bravecto chewable tablets, Bravecto spot-on and the 12-month Bravecto injection all contain fluralaner, but the way the drug enters the body, its release rate and its pharmacokinetics are very different.

When assessing a tick-control product, it is therefore useful to look at at least three things:

route of administration → active substance → where the active substance goes after administration.

Comparison tables

If you do not want to read the entire article, use the comparison tables below to compare mechanisms of action, duration, adverse effects, removability and possible effects on other family members. More detailed explanations and sources are provided in the relevant sections of the article.

The tables are deliberately concise: ‘main adverse effects’ is not a complete list of all adverse effects in the official product information, and the ‘what it covers / why use it’ column summarises the main practical indications. Exact indications, frequencies and sources are provided in the relevant sections and in the official product information for each product.

How should adverse-effect frequencies be read? The frequency categories used in official product information correspond to defined ranges:

• very common means more than 1 animal in 10;
• common means 1 to 10 animals in 100;
• uncommon means 1 to 10 animals in 1,000;
• rare means 1 to 10 animals in 10,000;
• very rare means fewer than 1 animal in 10,000, including isolated reports.

These categories describe how often an adverse effect occurs, not how severe it is. ‘Rare’ answers the question ‘how often?’, not ‘how serious?’

It is also important not to assume that a frequency category in the product information means every adverse effect was measured in a controlled study of at least 10,000 animals. Pre-authorisation studies are often too small to detect rare adverse effects. Some safety signals only emerge through pharmacovigilance after widespread use, and with spontaneous reporting the true incidence may remain unknown.

Collars

Why are they used? They provide long-lasting external treatment, with one major practical difference from a tablet or injection: the source of the active substance can be physically removed. At the same time, the active substance is usually present on the dog’s coat throughout the wearing period.

Collars: effect, duration and removability

Product	Active ingredient(s)	What it covers / why use it	Duration	Removability
Foresto / Seresto	imidacloprid + flumethrin	Fleas and ticks; long-term external protection. Active substances are continuously released onto the skin and coat.	Fleas 7–8 months; ticks up to 8 months.	Yes. The collar can be removed; active substance already distributed on the coat does not disappear immediately.
Scalibor	deltamethrin	Ticks; also repellent/anti-feeding activity against sand flies and mosquitoes.	Ticks 5–6 months; sand flies 5–6 months; mosquitoes up to 6 months.	Yes. The Estonian marketing authorisation ended in 2023, but the product is still used elsewhere in Europe.
Kiltix	propoxur + flumethrin	Ticks and fleas; active substances are released from the collar onto the coat.	Depending on the version, up to 6–7 months.	Yes. The collar can be removed immediately if problems occur; substance already distributed on the coat does not disappear at once.

Collars: adverse effects and impact on family members

Product	Main adverse effects	Family members / other animals	Special considerations / environment
Foresto / Seresto	Local skin reactions; official information also describes gastrointestinal and behavioural signs and rare/very rare neurological signs.	Active substances are released onto the skin and coat throughout the wearing period. Avoid prolonged contact with the collar and the dog wearing it; the dog should not sleep with the owner, especially a child.	Hazardous to aquatic organisms; used collars must not enter waterways.
Scalibor	Rare local skin reactions; very rare behavioural, gastrointestinal and neurological signs, including ataxia and tremor.	Avoid prolonged contact with the collar and the dog wearing it, including sleeping together; this is particularly important for children. Children under 2 years should not touch or put the collar in their mouth. Do not use in cats.	Remove the collar before swimming/washing; avoid swimming during the first 5 days after fitting.
Kiltix	Very rare skin reactions and behavioural changes; oral exposure may cause salivation, vomiting and diarrhoea.	Propoxur is a carbamate cholinesterase inhibitor. Wash hands after fitting the collar. Children should avoid contact with the animal wearing the collar; infants and small children should be kept away.	Very toxic to birds, bees and aquatic organisms; avoid swimming in waterways.

Spot-on products applied to the skin

Why are they used? They are applied periodically to the skin. It is important to know that some spot-ons act mainly on the skin/coat, while others are absorbed systemically. The term ‘spot-on’ alone does not tell you where the active substance goes after application.

Spot-on products: effect, duration and removability

Product	Active ingredient(s)	What it covers / why use it	Duration	Removability
Advantix	imidacloprid + permethrin	Fleas and ticks; permethrin adds repellent activity against ticks and some flying insects.	Ticks about 3–4 weeks; fleas about 4 weeks.	Limited. Once spread across the skin, the product cannot be completely removed.
Frontline Tri-Act	fipronil + permethrin	Fleas and ticks; permethrin adds repellent/anti-feeding activity against several flying insects.	Ticks and fleas about 4 weeks.	Limited. Once distributed, the treatment cannot simply be ‘switched off’.
Vectra 3D	dinotefuran + permethrin + pyriproxyfen	Fleas and ticks; repellent activity; pyriproxyfen inhibits development of flea eggs/larvae.	Ticks about 3–4 weeks; fleas 1 month; inhibition of flea reproduction up to 2 months.	Limited. Once distributed, the product is not simply removable.
Frontline Spot On	fipronil	Fleas and ticks; activity mainly at skin and coat level.	Fleas up to 8 weeks; ticks up to 4 weeks.	Limited. Systemic absorption is low, but the substance persists in skin/coat structures.
Bravecto Spot-On	fluralaner	Fleas and ticks; applied to the skin but systemically absorbed isoxazoline.	Up to 12 weeks.	Not removable after systemic absorption; very early washing may reduce the amount still on the surface.
Prac-tic	pyriprole	Fleas and ticks; phenylpyrazole, acting mainly by contact.	About 4 weeks.	Limited. Absorption of the parent compound is low, but active metabolites are systemically available.

Spot-on products: adverse effects and impact on family members

Product	Main adverse effects	Family members / other animals	Special considerations / environment
Advantix	Local reactions and gastrointestinal signs; very rare behavioural or neurological signs.	Avoid handling until dry, especially by children; a recently treated dog should not sleep with the owner/child. Permethrin is dangerous to cats.	A treated dog should not enter waterways for at least 48 hours.
Frontline Tri-Act	Very rare local reactions, gastrointestinal signs and reversible neurological signs, including tremor/ataxia.	Permethrin is dangerous to cats. Because of NMP there are specific warnings for pregnant women/women who may be pregnant and a recommendation for protective gloves for women of childbearing potential.	Children should not play with the dog until dry; a recently treated animal should not sleep with the owner, especially a child.
Vectra 3D	Rare local reactions, behavioural changes and tremor; very rare vomiting, diarrhoea, ataxia and seizures.	Permethrin is dangerous to cats. NMP leads to specific pregnancy and handling instructions; keep children away for at least 4 hours.	A treated dog should not enter waterways for 48 hours.
Frontline Spot On	Very rare local skin reactions; salivation may occur after licking and rare reversible neurological signs have been described.	Avoid contact until the application site is dry; a treated animal should not sleep with the owner, especially a child. Do not use in rabbits.	Fipronil may harm aquatic organisms; avoid swimming according to the product information.
Bravecto Spot-On	Common mild application-site reactions; very rare gastrointestinal, pruritic and neurological signs such as tremor, ataxia and seizures.	Do not touch the application site until it is no longer noticeable; this may take up to 48 hours. Avoid hugging and bed-sharing during this period.	A treated dog should not enter waterways for 48 hours.
Prac-tic	Very rare skin, gastrointestinal and general signs; ataxia and seizures have been described.	Avoid direct contact until the application site is dry; contact with skin/mucosa may cause irritation or numbness.	Pyriprole may harm aquatic organisms.

Sprays

Why are they used? The whole coat is treated externally. During spraying, avoiding inhalation and skin contact with the product becomes particularly important.

Sprays: effect, duration and removability

Product	Active ingredient	What it covers / why use it	Duration	Removability
Frontline Spray	fipronil	Fleas and ticks; the whole coat is treated externally.	Ticks up to 1 month; fleas in dogs up to 3 months.	Limited. Systemic absorption is minimal, but fipronil remains on the coat for weeks.

Sprays: adverse effects and impact on family members

Product	Main adverse effects	Family members	Special considerations / environment
Frontline Spray	Very rare local reactions; possible salivation, vomiting, respiratory signs and reversible neurological signs.	During spraying and until the coat is completely dry, avoid handling and play with children; a recently treated animal should not sleep with the owner, especially a child. Fipronil remains on the coat for a long time after drying, although the official information does not require avoiding normal stroking once dry. After prolonged or intensive contact, washing hands before eating or touching the face is still sensible.	Good ventilation and protective gloves are required. Do not use in rabbits; keep out of waterways for 2 days.

Chewable tablets: single-ingredient systemic products

Why are they used? They provide systemic activity without leaving a persistent layer of active substance on the coat. With isoxazolines, a tick or flea generally has to attach and feed in order to be exposed to the active substance. Once swallowed, the product can no longer be physically removed.

Neurological adverse effects of isoxazolines

Isoxazolines are a group of flea and tick medicines that includes fluralaner, afoxolaner, sarolaner and lotilaner. Put simply, they act on the parasite’s nervous system: they disrupt normal nerve signalling, leading to paralysis and death. These drugs were developed to act primarily on the nervous system of arthropods, but that does not mean neurological adverse effects in dogs are impossible. Muscle tremor, ataxia and seizures have been reported in dogs treated with isoxazolines, including seizures in dogs with no previous history of them.

Depending on the product, official isoxazoline product information lists neurological adverse effects such as muscle tremor, ataxia and seizures. For most products discussed here, these are classified as very rare.

That context matters.

‘Very rare’ does not mean the reaction is common, but it also does not mean it cannot happen. The FDA has specifically noted that seizures have been reported even in dogs with no previous seizure history. For that reason, several isoxazoline product labels recommend particular caution in dogs with existing neurological problems or epilepsy.

 

Single-ingredient tablets: effect, duration and half-life

Product	Active ingredient	What it covers / why use it	Duration	Half-life / removability
Bravecto chewable tablet	fluralaner	Fleas and ticks; systemic isoxazoline.	Ticks 8–12 weeks depending on species; fleas up to 12 weeks.	about 12 days; not removable.
NexGard	afoxolaner	Fleas and ticks; systemic isoxazoline.	Ticks about 1 month; fleas at least 5 weeks.	about 2 weeks; not removable.
Frontpro	afoxolaner	Same active ingredient as NexGard; over the counter in Estonia.	Ticks about 1 month; fleas at least 5 weeks.	about 2 weeks; not removable.
Simparica	sarolaner	Fleas and ticks; systemic isoxazoline.	At least about 5 weeks.	about 11–12 days; not removable.
Credelio	lotilaner	Fleas and ticks; systemic isoxazoline.	About 1 month.	about 4 weeks; not removable. Give with or after food.
AdTab	lotilaner	Same active ingredient as Credelio; over the counter in Estonia.	About 1 month.	about 4 weeks; not removable. Give with or after food.

Single-ingredient tablets: adverse effects and special considerations

Product	Main adverse effects	Special considerations	Family members
Bravecto chewable tablet	Common mild gastrointestinal signs (reduced appetite, salivation, diarrhoea, vomiting); very rare tremor, ataxia and seizures.	Use caution in dogs with existing epilepsy. Because of the long duration, the source of active substance cannot be removed if an adverse effect occurs.	After swallowing, active substance does not remain on the coat; keep the tablet away from children and wash hands after handling.
NexGard	Very rare gastrointestinal signs, lethargy, reduced appetite and pruritus; seizures, ataxia and tremor have also been described.	Half-life varies; in one Collie study, persistence was substantially longer at a high dose.	The main family-member risk is accidental ingestion of the tablet itself; keep away from children.
Frontpro	Same active-substance class as NexGard and a similar profile of very rare neurological reactions.	Over-the-counter status does not make the product pharmacologically ‘milder’.	Keep away from children; wash hands after handling.
Simparica	Very rare vomiting/diarrhoea, lethargy, reduced appetite, tremor, ataxia and seizures.	Systemic and not removable; the individual dog’s neurological history matters.	No persistent active-substance layer remains on the coat after swallowing; keep tablets away from children.
Credelio	Very rare gastrointestinal and general signs; ataxia, tremor and seizures have been described.	Half-life is about 4 weeks, so the previous dose is not necessarily eliminated by the time the next monthly dose is given.	Keep away from children; wash hands after handling.
AdTab	Same active-substance class as Credelio and a similar safety profile; neurological reactions are described as very rare.	Over the counter. Lotilaner’s long half-life does not change with prescription status.	Keep away from children; wash hands after handling.

Chewable tablets: combination products

Why are they used? When a dog needs treatment against external and internal parasites at the same time. A broader spectrum does not automatically mean a better choice; official information for several combination products recommends using them specifically when treatment or prevention against the different parasite groups is needed simultaneously.

Combination tablets: what they cover, duration and removability

Product	Active ingredients	What it covers / why use it	Duration against external parasites	Half-life / removability
NexGard Spectra	afoxolaner + milbemycin oxime	Ticks/fleas + several gastrointestinal nematodes; also heartworm and certain lungworm indications according to the official product information. Use when both external- and internal-parasite activity is needed.	Ticks about 4 weeks; fleas about 5 weeks.	Not removable; afoxolaner about 2 weeks, milbemycin oxime substantially shorter.
Simparica Trio	sarolaner + moxidectin + pyrantel	Ticks/fleas/mites + gastrointestinal nematodes; also heartworm and angiostrongylosis prevention/treatment according to the indications.	Ticks about 4–5 weeks; fleas about 5 weeks.	Not removable; sarolaner about 12 days, moxidectin about 11 days.
Credelio Plus	lotilaner + milbemycin oxime	Ticks/fleas + several gastrointestinal nematodes; combination product for mixed infestation or risk of mixed infestation.	About 1 month.	Not removable; lotilaner about 24 days. Official information describes slight accumulation with monthly use.
Bravecto CombiUNO	fluralaner + milbemycin oxime	Ticks/fleas + gastrointestinal nematodes, with lungworm and/or heartworm indications. Intended for mixed infestation or risk of mixed infestation.	Ticks and fleas about 1 month.	Not removable; fluralaner about 11 days. Accumulation has been described with repeated monthly administration.

Combination tablets: adverse effects and special considerations

Product	Main adverse effects	Special considerations	Family members
NexGard Spectra	Uncommon gastrointestinal signs, lethargy, reduced appetite and pruritus; very rare redness, seizures, ataxia and tremor.	Milbemycin oxime is a P-gp substrate. Several finished products containing milbemycin have been assessed as safe in MDR1* dogs at label doses; dosing must be followed strictly, and interactions with other P-gp substrates or macrocyclic lactones require assessment.	After swallowing, there is no continuous coat-based exposure; keep tablets away from children.
Simparica Trio	Very rare vomiting, diarrhoea, lethargy, reduced appetite, tremor, ataxia and seizures.	Use the combination only when activity against different parasite groups is needed at the same time. An MDR1* variant does not automatically mean the product is contraindicated; label dosing must be followed strictly.	Keep tablets away from children; wash hands after handling.
Credelio Plus	Uncommon behavioural and gastrointestinal signs, tremor, pruritus, reduced appetite and lethargy; very rare ataxia and seizures.	Follow label dosing strictly; an MDR1* variant does not automatically mean the product is contraindicated. Lotilaner accumulation with monthly use is specifically described in the official information.	Keep away from children; give with or after food.
Bravecto CombiUNO	Common vomiting; uncommon diarrhoea, salivation, retching, lethargy and reduced appetite; rare blood in faeces; very rare tremor, ataxia and seizures.	Neurological reactions can be serious; use caution in dogs with epilepsy. The presence of milbemycin oxime does not automatically make the product contraindicated in MDR1* dogs; follow the label dose and the official information for the specific product.	Keep away from children; wash hands after handling the tablet.

*MDR1, or an ABCB1 gene variant, can alter a dog’s sensitivity to certain medicines. See the MDR1 section for a fuller explanation and the list of breeds at risk.

Long-acting injections

Why are they used? They provide very long-lasting systemic activity without repeated administration at home. The trade-off is that once injected, the product cannot be removed, and release and elimination of the active substance continue for a long time.

Long-acting injection: effect and pharmacokinetics

Product	Active ingredient	What it covers / why use it	Duration	Pharmacokinetics / removability
Bravecto 150 mg/ml injection	fluralaner	Systemic isoxazoline; long-acting subcutaneous formulation against ticks and fleas.	Up to 12 months. Median Cmax around day 37.	Not removable. Blood half-life in 6-month-old dogs approximately 92–170 days.

Long-acting injection: adverse effects and special considerations

Product	Main adverse effects	Special considerations	Family members / user safety
Bravecto 150 mg/ml injection	Common injection-site swelling; uncommon reduced appetite, tiredness and mucosal hyperaemia; rare vomiting/diarrhoea; very rare tremor, ataxia, seizures, hypersensitivity and pruritus.	Use caution in dogs with existing epilepsy; use in dogs under 6 months is restricted according to the product information because of limited data.	No persistent active-substance layer remains on the coat at home. The medicine is administered by a veterinarian or under their direct supervision; user safety focuses especially on avoiding accidental self-injection.

An adverse effect does not have to appear after the first dose

It can be easy for an owner to associate an adverse effect with a medicine when a dog receives a new product for the first time and a new symptom appears within hours or days.

It is much harder to recognise the connection when the first dose appears to cause no problem, the second does too, and tremor, ataxia or a seizure develops only after a later dose or after a longer delay.

A 2024 poison-centre case analysis published in Veterinary Record found that the interval between isoxazoline exposure and the onset of neurological signs can be prolonged.

The authors noted that this delay can make the connection between the medicine and the symptom easier to miss. This is also important from a pharmacovigilance perspective.

If neither the owner nor the veterinarian connects the symptom with the medicine, the case may never reach the pharmacovigilance system. Previous doses being tolerated without problems should therefore not be treated as proof that a later adverse effect is impossible.

FendaF’s own experience also illustrates why an individual dog’s reaction cannot be predicted with certainty from population data. Oscar received Bravecto for the first time without any obvious problem. After the next dose he developed skin problems, and recovery became a very long process lasting years. In retrospect it is not possible to prove that Bravecto caused the problems, but neither is it possible to prove that the medicine was unrelated. We therefore describe this as a possible medicine-related reaction, not a proven causal relationship. Oscar’s experience also shows why a previously well-tolerated dose does not guarantee that the next administration will not trigger a reaction.

What does a drug’s half-life mean?

Half-life is one of the terms that can easily be misunderstood when discussing tick-control products.

A drug’s half-life is not the time after which the drug has disappeared from the body. It is approximately the time required for the concentration of the active substance to decrease by half.

Credelio example

Take lotilaner, the active substance in Credelio, whose terminal half-life in dogs is approximately four weeks. Credelio is also administered about once a month.

If we deliberately use a highly simplified mathematical example and imagine that the active-substance level after the first dose is 100 units, then after one half-life, or roughly four weeks, about 50 units would remain.

When the next dose is given, the body therefore does not start again from an assumed zero.

A simplified mathematical model would look something like this:

Dose 1: 100

after 4 weeks: 50

new dose added: 150

after 4 weeks: 75

new dose added: 175

before the next dose: 87.5

new dose: 187.5

and so on.

This does not mean that these exact numbers would occur in a real dog’s blood. Pharmacokinetics are affected by absorption, tissue distribution, metabolism, food, individual elimination and many other factors.

The purpose of the example is to explain one principle: ‘the medicine is given once a month’ does not mean ‘the previous dose has disappeared from the body by the end of the month’.

What is accumulation?

If a medicine is given again before the previous dose has been fully eliminated, repeated dosing can lead to accumulation of the active substance.

Accumulation does not automatically mean toxic or dangerous build-up. Official dosing schedules and safety studies are designed with repeated administration in mind. Safety studies tell us how a medicine behaves in dogs generally, or what might be expected in an ‘average’ dog. They cannot predict exactly how your individual dog will react.

The Homeostasis Fairy™ reminds us: the average dog does not live in your home.

Drug-safety data describe how often different reactions occurred in the dogs that were studied. Your dog, however, is one specific individual with its own age, health background, genetics, medicines and tolerance.

Accumulation does mean, however, that each new dose may not arrive at a point when the body is completely ‘clear’ of the previous one.

This is not only theoretical mathematics.

For example, the official product information for Credelio Plus states the following for lotilaner:

• terminal half-life of approximately 24 days;
• slight accumulation is observed with repeated monthly administration;
• steady state is reached after the fourth monthly dose.

The official information for some monthly combination products containing fluralaner also specifically describes accumulation with repeated administration.

It is therefore worth distinguishing between:

• duration of effect;
• dosing interval;
• half-life;
• the time during which the active substance can still be present in the body.

These are not the same thing.

Quick comparison of half-life and accumulation

Product	Active ingredient	Dosing interval / protection	Approximate half-life	Accumulation / important note
Bravecto chewable tablet	fluralaner	8–12 weeks of protection	about 12 days	Duration of clinical effect and plasma half-life are not the same thing.
NexGard / Frontpro	afoxolaner	about 1 month	about 2 weeks	Individual variability can be substantial; in one Collie study, up to 47.7 days was measured at a high dose.
Simparica	sarolaner	about 1 month	about 11–12 days	Monthly systemic administration.
Credelio / AdTab	lotilaner	about 1 month	about 4 weeks	The previous dose is not necessarily eliminated when the next monthly dose is due.
Credelio Plus	lotilaner + milbemycin oxime	about 1 month	lotilaner about 24 days	According to official product information: slight accumulation; steady state after the 4th monthly dose.
Bravecto CombiUNO	fluralaner + milbemycin oxime	about 1 month	fluralaner about 11 days	According to official product information: accumulation observed with repeated monthly administration.
Bravecto injection	fluralaner	up to 12 months	about 92–170 days (in 6-month-old dogs)	Median Cmax around day 37; the long-acting injection is not directly comparable with monthly tablets.

Can accumulation increase the risk of adverse effects?

Pharmacologically, accumulation means that systemic exposure after repeated dosing may differ from exposure after the first single dose. It is therefore theoretically possible that changing exposure could influence the occurrence or severity of adverse effects.

Current data do not allow us to claim, for example, that ‘the seizure risk is twice as high with the third dose as with the first’.

Such an increase in risk has not been quantified sufficiently well.

Two statements therefore need to be kept separate: accumulation and changing systemic exposure can be pharmacokinetically documented facts, but those facts alone cannot be used to calculate the probability of a specific adverse effect.

They do, however, help explain why a reaction after a later dose should not automatically be dismissed simply because earlier doses caused no obvious adverse effects.

Bravecto: the same active substance, a very different journey through the body

Fluralaner is a particularly good example of why a product should not be described only by the name of its active substance.

Bravecto chewable tablet: the dog swallows a tablet and fluralaner is absorbed systemically from the gastrointestinal tract. Tick-control activity lasts up to 12 weeks depending on the tick species. Once absorbed, the product cannot be physically removed.

Bravecto Spot-On: the product is applied to the skin. At first glance it may look similar to other topical spot-on products, but fluralaner is absorbed systemically through the skin. So ‘spot-on’ does not mean that the effect is confined to the skin or coat. Once the active substance has been absorbed, washing cannot remove it from the body.

Bravecto 12-month injection: the purpose of the subcutaneous fluralaner injection is to provide activity against ticks and fleas for up to 12 months. Its pharmacokinetics differ substantially from the chewable tablet. According to the official product information, the median maximum blood concentration of fluralaner is reached only around day 37 after injection. In young dogs, the measured half-life was approximately 92–170 days, or roughly three to five and a half months.

Remember: half-life does not mean that the substance has disappeared from the body after that period. After one half-life, the level has fallen by approximately half.

Once administered, the injection cannot be removed.

So alongside the convenience of ‘one injection a year’, it is worth considering the pharmacokinetic profile of the systemic product being used.

Combination products: does the dog need every active ingredient?

There are more and more products on the market that combine tick and flea control with activity against internal parasites.

Examples:

• NexGard Spectra: afoxolaner + milbemycin oxime
• Simparica Trio: sarolaner + moxidectin + pyrantel
• Credelio Plus: lotilaner + milbemycin oxime
• Bravecto CombiUNO: fluralaner + milbemycin oxime

It is important to understand that an additional active ingredient does not necessarily make a product a ‘better tick treatment’. For example, NexGard Spectra’s activity against ticks still comes from afoxolaner. Milbemycin oxime adds activity against internal parasites.

The official information for several combination products says essentially the same thing: the product should be used when the dog simultaneously needs the different types of parasite control provided by its active ingredients. If that combined risk is not present, a narrower-spectrum product is recommended.

This principle matters. When choosing parasite control, the question should not be ‘Which product covers the most?’ but ‘Which effects does this particular dog actually need right now?’

Adverse effects of Bravecto CombiUNO

One of the newer combination products is Bravecto CombiUNO, which contains fluralaner and milbemycin oxime.

Its official product information classifies adverse effects as follows:

• common, 1–10 animals in 100: vomiting;
• uncommon, 1–10 animals in 1,000: diarrhoea, hypersalivation, retching, lethargy and decreased appetite;
• rare, 1–10 animals in 10,000: blood in the faeces;
• very rare, fewer than 1 animal in 10,000 including isolated reports: muscle tremor, ataxia and seizures.

According to the product information, gastrointestinal adverse effects usually resolve within one day, and lethargy and reduced appetite usually within two days. Neurological reactions can be serious.

The product information specifically notes that neurological reactions can be serious. That does not mean they occur in a large proportion of treated dogs.

Frequency categories should be read exactly as they are presented in the official product information.

Over-the-counter does not mean risk-free

Some systemic isoxazolines are available over the counter in Estonia. For example, Frontpro contains afoxolaner and AdTab contains lotilaner.

The official safety information for both active substances describes very rare neurological reactions.

It is therefore not correct to conclude: ‘If I can buy it without a prescription, it must be practically risk-free.’

Prescription status concerns how a medicine is supplied. It does not change the biological mechanism of action of the drug.

Effects on other family members: what does ‘safe’ mean in a real home?

Choosing a parasite-control product does not always concern only the dog. With topical products in particular, active substances may remain on the dog’s skin or coat after application, while a medicated collar can release them continuously for months. In addition to the dog’s safety, it is therefore worth considering who shares the home and how they interact with the dog in everyday life.

• children;
• pregnant people;
• other dogs;
• cats;
• and, in some cases, the aquatic environment.

Why are the warnings about small children so specific?

A small child does not touch a dog the way an adult does. They stroke and hug the dog, touch the collar, put their hands in their mouth, eat with their hands and may sleep in the same bed as the dog. Hand-to-mouth exposure is therefore much more likely in practice. The official information for several products explicitly says that children should not play with a recently treated animal until the application site is dry and that a recently treated animal should not sleep in the owner’s bed, especially with children. For the Foresto/Seresto medicated collar, the information specifically states that the active substances are released onto the skin and coat throughout the wearing period and that the dog should not sleep in the same bed as the owner, especially a child.

Route of administration	How can a family member be exposed to the active substance?	Practical meaning
Medicated collar	The collar continuously releases active substance onto the dog’s skin and coat. Exposure is not limited to the day the collar is fitted.	A small child should not play with the collar or put it in their mouth. Several collars advise avoiding sleeping in the same bed as the dog, especially for children. Wash hands after fitting the collar.
Spot-on or spray	The greatest direct exposure is during application and while the application site or coat is still wet. Sprays add the possibility of inhalation.	Children should not play with the treated animal until dry. Several products recommend treating in the evening and avoiding bed-sharing with a recently treated animal. With sprays, ensure ventilation and avoid inhaling the aerosol.
Oral tablet	After swallowing, the active substance does not remain on the coat in the same way as with a collar or spot-on.	The main family-member risk is accidental ingestion or handling of the tablet, especially by a child. Keep the medicine out of children’s reach and wash hands after handling.
Injection	After injection, no persistent active-substance layer remains on the dog’s coat at home.	Direct exposure of family members is generally lower than with topical products; the main safety question here is the dog’s own long-term systemic exposure.

If someone in the home is pregnant, has asthma or is hypersensitive

Not every ‘health problem’ can be grouped into one risk category. Some products, however, have very specific user-safety warnings. Frontline Tri-Act and Vectra 3D contain N-methylpyrrolidone (NMP), which leads to separate handling instructions for pregnant women or women who may be pregnant, and to a recommendation that women of childbearing potential use protective gloves. The Frontline Spray information warns that people with known sensitivity or asthma may be particularly sensitive to the product. Several topical products also advise avoiding exposure in people with known hypersensitivity.

For an immunocompromised, very elderly or otherwise infection-susceptible family member, a different issue is the zoonotic risk from parasites. This does not automatically mean a tick-control product is chemically more toxic to that person, but the dog’s parasite status, prompt removal of faeces, flea control and hand hygiene become even more important. The CDC considers children under five, immunocompromised people and older adults to be at increased risk from several infections that can spread from animals to people.

SAFETY BOX: don’t stroke the dog and then eat a sandwich with the same hand • Read the leaflet for the specific product: user-safety instructions vary more than you might expect. • Do not eat, drink or smoke while applying a spot-on or spray. Wash your hands thoroughly afterwards. • If you have touched a wet application site, medicine-damp coat or a medicated collar/collar area, wash your hands before handling food or eating. In other words: not dog → hand → apple or sandwich. • Do not let a small child stroke a recently treated animal or play with a medicated collar. Keep pipettes and tablets completely out of children’s reach. • If the leaflet says the treated animal should not sleep in the owner’s bed, that sentence is not decorative. This is especially important for children; with a medicated collar, active substance can remain on the coat throughout the wearing period. • If someone in the household is pregnant, has a known chemical or skin sensitivity, or has asthma, read the section on precautions for the person administering the veterinary medicine before choosing a product, not only the section on adverse effects in the dog.

Permethrin and cats

Cats and dogs each have their own products, but if the thought is ‘I have some left over from the dog, I’ll use it on the cat’, it is important to know that permethrin can cause severe neurological signs in cats and poisoning can be life-threatening.

A cat should not lick the application site of a recently treated dog, and the animals should be kept apart if necessary until the product is dry.

That is why households with cats need to take this into account when using Advantix, Frontline Tri-Act and Vectra 3D.

Frontline Tri-Act, Vectra 3D and NMP

The product information for some spot-on products contains a specific warning about the excipient N-methylpyrrolidone, or NMP.

Animal studies have found fetotoxicity with NMP.

For that reason, the product information includes specific handling warnings for women who are pregnant or may be pregnant and recommends protective gloves for women of childbearing potential.

This is a good example of why the table column ‘impact on other family members’ is not a cosmetic extra.

Removability: a property that is rarely discussed

A low population frequency of an adverse effect does not mean that the risk for one particular dog can be predicted. The question is therefore not only how rare an adverse effect is, but also how much benefit the medicine offers, how serious a possible reaction could be and what level of risk the individual owner considers acceptable for their dog.

For every medicine, it is worth asking: does my dog need this medicine right now, and is there another suitable way to achieve the same goal? Sometimes a medicine may be unavoidable and its benefits clearly outweigh its possible risks. In another situation, a different risk-management strategy may be possible. The same risk does not carry the same weight in every situation or for every dog.

If an adverse effect occurs, there is a major practical difference between a product whose source can be removed and one whose source cannot.

Collar: it can be taken off, which stops further release of active substance from the collar.

Spot-on: very early after application, washing may reduce the amount of product remaining on the surface of the skin or coat. Once the product has spread or has been absorbed systemically, however, it cannot be completely ‘washed off’.

Tablet: once the tablet has been swallowed and the active substance absorbed, the product cannot be physically removed from the body. It does not leave a persistent active-substance layer on the coat, so exposure of family members is lower than with topical products. From the dog’s point of view, however, a systemic product is not removable after absorption. If an adverse effect occurs, exposure cannot be stopped by removing the tablet or washing the dog; elimination depends on the pharmacokinetics of the specific drug.

Long-acting injection: the same principle applies even more clearly to an injection designed to release the active substance over a long period. After administration, the body has to eliminate the active substance gradually on its own.

Removability is therefore worth considering as a separate parameter, not merely as a matter of convenience.

Environmental impact

Tick-control products do not necessarily affect only the dog and the tick.

Several active substances are hazardous to aquatic organisms.

The official information for products containing fipronil, permethrin, deltamethrin and several other active substances contains specific warnings about swimming, waterways or disposal of medicinal waste.

For example, the product information may require that a dog not swim for a certain period after treatment. A used medicated collar must not be discarded in nature or in water; disposal should follow the specific package leaflet and local instructions for medicinal waste.

Environmental risk deserves particular attention for dogs that swim regularly in lakes, rivers or the sea.

What about ‘natural’ tick control?

‘Natural’ does not automatically mean effective or safe. At the same time, it is not sensible to judge every natural tick-control method by exactly the same measure used for medicines that kill ticks, because the proposed mechanisms may be different.

For an acaricide, an important measure may be how quickly a tick dies. A repellent, in contrast, aims to reduce the likelihood that a tick comes onto the animal, remains there or attaches. Diatomaceous earth works physically, and its proposed effect differs from both a repellent and a systemic medicine. Evidence therefore needs to be assessed according to what each method actually claims to do.

Meghan Barrett’s integrative approach

In her 2024 Holistic Dog Care Summit 2.0 presentation ‘Natural Flea & Tick Control’, integrative veterinarian Meghan Barrett discussed environmental modification, plant-based repellents, properly diluted essential oils, apple cider vinegar, garlic and diatomaceous earth as parts of a natural parasite-control approach. For the environment, she emphasised measures such as keeping grass short and removing leaves and other debris to reduce shady habitats suitable for fleas and ticks.

For oral approaches, Barrett mentioned garlic, brewer’s yeast and apple cider vinegar. Her explanation was that the aim is to alter the dog’s body or skin odour in a way that makes the animal less attractive to parasites. For apple cider vinegar, she gave a specific practical amount of 1 teaspoon per approximately 950 ml of drinking water. For topical use, she suggested diluting apple cider vinegar with water in a 1:1 ratio.

These amounts are presented here as practical recommendations from Barrett’s presentation, not as parasite-control doses confirmed in clinical studies in dogs. With garlic, safe quantities matter, and when a commercial garlic-containing product is used the amount on the label should be followed. Larger or concentrated amounts of garlic can cause Allium toxicosis and haemolytic anaemia in dogs, so ‘natural’ does not automatically mean risk-free.

Barrett’s balance of risks

Barrett framed parasite control as weighing two risks. She noted that many diseases transmitted by fleas and ticks are treatable, whereas a very severe reaction to a pesticide can be irreversible. In her view, there may therefore be situations in which it is more reasonable to accept the risk of an infectious disease and treat it if necessary than to keep a dog under continuous chemical parasite control. Barrett emphasised that the decision ultimately belongs to the owner.

This is Barrett’s risk assessment, not a universal recommendation. Tick-borne diseases can also be severe, prolonged or, in rare cases, life-threatening, and dogs differ in both exposure and health risk. The point is that the decision is not based on one risk alone: parasite exposure, possible disease risk, the adverse-effect profile of the chosen product, frequency of exposure and the individual dog’s background all belong on the same scale.

Non-chemical and physical methods

Diatomaceous earth

Diatomaceous earth is also used externally in integrative practice against fleas and ticks. Its action is physical and depends on the powder being dry: fine particles damage the protective outer layer of arthropods and promote desiccation. Dust should not be inhaled or allowed into the eyes or mucous membranes, and diatomaceous earth can also dry the skin.

At FendaF, diatomaceous earth has been one of the practical non-medicinal tools we have used. As with other methods, personal experience cannot be converted into a precise efficacy percentage for every dog. We have used a diatomaceous-earth suspension (powder diluted in water), because this avoids airborne dust and the associated inhalation risk.

Garlic

The evidence around garlic is more nuanced than a simple ‘works’ or ‘does not work’. Garlic extract has shown tick-repellent activity in laboratory testing, but good in vivo dog studies showing how well an amount that is safe for a dog repels ticks in real life are scarce. A 2020 systematic evidence search found no suitable in vivo studies in dogs for garlic and fleas. The absence of studies is a knowledge gap, not a negative study result.

Plant- and essential-oil-based tick-control products

There is a substantial body of research on plant- and essential-oil-based tick-control products. A 2025 systematic review covered more than one hundred studies of plant acaricides and repellents. In a 2026 field study in free-roaming dogs, a PMD-rich Eucalyptus citriodora oil-based spot-on markedly reduced tick burden even though the laboratory test did not show a tick-killing effect. This is a good example of why the effectiveness of a repellent cannot be judged only by tick mortality.

Essential oils can cause poisoning

Essential oils are biologically active chemicals.

They can be absorbed through:

• the skin;
• the gastrointestinal tract;
• the respiratory tract;
• and mucous membranes.

The Merck Veterinary Manual notes that concentrated essential oils should not be applied directly to an animal.

Signs reported in dogs with essential-oil poisoning include:

• vomiting,
• lethargy,
• hypersalivation,
• ataxia,
• tremor,
• seizures,
• skin irritation,
• and, in more severe cases, liver or kidney injury.

Particularly problematic oils can include tea tree oil, pennyroyal, wintergreen and some other highly concentrated essential oils.

So the correct contrast is not ‘medicine = chemical = dangerous’ and ‘essential oil = natural = safe’.

In both cases, the substance, dose, concentration and individual animal matter.

A ready-made product is not automatically safe either

Experimenting with essential oils at home can be risky if you do not know how, or with what, they should be diluted. But the opposite conclusion is also unsafe: ‘If it is sold in a shop, it must be safe and correctly formulated.’

The quality of commercial products can vary.

It is important to know:

• which essential oils are used;
• their quality and purity;
• the concentration in which they are used;
• whether the dilution is correct;
• which carrier oil is used;
• whether the safety of the finished formulation has been assessed in dogs.

The word ‘natural’ on the package is not a quality-control system.

Ultrasonic tags, amber necklaces and other ‘chemical-free’ solutions

An interesting 2026 field study compared, among other things, the following in free-roaming dogs:

• an ultrasonic device;
• an amber necklace;
• a ceramic-bead collar;
• a plant-based collar;
• and a plant-based spot-on containing PMD.

Under the study conditions, the tested ultrasonic, amber and ceramic-bead products showed no measurable protective effect against ticks compared with the control group.

The plant-based spot-on, on the other hand, markedly reduced tick burden.

The study was small and took place in Mali under conditions of very high natural parasite pressure, so it cannot be used to conclude that every such product is incapable of having any effect in every possible situation.

It is nevertheless reasonable to ask: what exactly in this product is supposed to affect the tick?

If the answer is ‘ultrasound’, ‘electromagnetic resonance’, ‘static electricity’ or another mechanism, it is worth checking whether the product’s effectiveness has actually been demonstrated in a controlled study.

Repellents used in integrative practice and the evidence

The same principle applies to garlic, lemon preparations, essential oils and other repellents used in integrative practice: the amount and quality of evidence vary greatly between methods. Some plant substances have laboratory or field studies behind them; others are used mainly on the basis of integrative veterinary practice and owner experience. A shortage of controlled dog studies does not itself prove that a method does not work; it means the size, duration and repeatability of the effect have not been established as precisely.

The amount of research also needs context. A manufacturer seeking approval for a registered veterinary medicine has a direct financial reason to fund large efficacy and safety studies. For an ordinary plant or a home method, the financial incentive can be much smaller, especially when the result cannot be protected as an exclusive product. ‘Less studied’ and ‘ineffective’ are therefore not synonyms.

At the same time, natural origin does not automatically mean safety or effectiveness. For every method, ask separately: what is it claimed to do, has that specific effect been studied, what experience exists, and what are the possible risks? Medicines and natural products deserve the same critical questions.

The lowest-tech tick control: check the dog

Among all this pharmacology, the simplest tool should not be forgotten: regularly checking the dog.

A tick that lands on a dog does not necessarily attach to the skin immediately. It may first move through the coat looking for a suitable place.

That means a very simple trick can sometimes help after a walk: a lint roller. A normal sticky clothes roller can be run over the surface of the coat after a walk in forest or long grass. A tick that is still moving freely on the coat may stick to the roller before it reaches the skin and attaches.

This is likely to work better on dogs with shorter, smoother coats. On long or very dense coats, the roller will not reach deeper layers.

So a lint roller does not replace a thorough tick check. It is simply one additional layer of risk management.

Areas worth checking especially carefully include:

• around the ears;
• the neck;
• the armpits;
• the groin;
• between the toes;
• and around the tail.

Any attached tick that is found should be removed as soon as possible with an appropriate tick-removal tool.

The Homeostasis Fairy asks: do we really need everything?

With parasite control it is very easy to drift into the mindset: ‘Just in case, let’s use something with the broadest possible spectrum and the longest possible duration.’

But dogs do not all live the same life.

One dog is in the forest every day. Another mainly walks on city streets. One travels to areas where heartworm or sand flies occur; another never leaves Estonia. One dog lives with cats, another with small children. One has a history of seizures, another may be at risk of an MDR1 mutation. The choice can also change if the household includes a small child, a pregnant person, someone with asthma or marked skin/chemical sensitivity, or someone who is severely immunocompromised. In such cases, the zoonotic risk from parasites and the user-safety instructions for the specific product need to be considered together.

What is the MDR1 mutation?

The current gene name is ABCB1, but in veterinary medicine the term MDR1 (multidrug resistance 1) is still very widely used. The gene encodes P-glycoprotein, a transporter that helps, among other things, to restrict the entry of certain drugs into the brain and to remove them from the body.

If a dog has a loss-of-function MDR1/ABCB1 variant, some drugs can reach the central nervous system in higher-than-usual concentrations and cause neurological toxicity. This is not a ‘disease’ but an inherited trait that can affect drug tolerance. It is most often discussed in Collies and other herding breeds, but the variant has also been found in breeds such as the German Shepherd and in mixed-breed dogs. An individual dog’s status can be established with a genetic test.

Which breeds can carry the MDR1/ABCB1 variant?

The current Washington State University / WADDL MDR1 breed table lists the following breeds and groups: Australian Shepherd, Australian Shepherd (Mini), Black Mouth Cur, Border Collie, Carolina Dog, Chinook, Collie, English Shepherd, German Shepherd, Golden Retriever, Herding Breed Cross, Long-haired Whippet, McNab, Mixed Breed, Old English Sheepdog, Shetland Sheepdog, Siberian Husky and Silken Windhound.

This does not mean that every dog of these breeds carries the variant. In the WSU data, frequency varies considerably, and for some listed breeds there are too few data to calculate a frequency or it is marked as unknown. The variant can also occur in mixed-breed dogs. A genetic test confirms an individual dog’s status.

See the Washington State University / WADDL MDR1 page for the breed table and drug-safety information.

In parasite control, MDR1 is especially relevant for certain drugs associated with P-glycoprotein, but the risk is not the same for every active substance or dose. According to Washington State University, label-directed use of afoxolaner, fluralaner, lotilaner or sarolaner has not been shown to increase adverse-effect risk in dogs with the MDR1 variant. Several finished products containing milbemycin or moxidectin have also been specifically evaluated as safe at label doses. This does not make MDR1 irrelevant: safety depends on the specific active substance, dose and product, and with some drugs or higher doses the variant can be clinically very important.

The practical conclusion is simple: with an MDR1-risk dog, do not alter doses ‘by eye’, use stronger concentrations intended for another animal species, or assume that the same active substance is equally safe at every dose. In breeds at risk, the individual dog’s ABCB1/MDR1 status can be determined by genetic testing, and drug choice should follow the official information for the specific product.

There is therefore no single product that is automatically ‘best for every dog’.

A better question is: what are this particular dog’s actual risks, and what is the narrowest suitable approach for reducing them?

When should you definitely speak to a veterinarian before choosing a parasite-control product?

An individual benefit-risk assessment is particularly important if the dog has:

• a history of seizures or another neurological disease;
• a previous reaction to a parasite-control product;
• an MDR1 mutation or risk of one;
• liver disease or another significant chronic illness;
• several medicines being used at the same time;
• pregnancy, lactation or breeding considerations;
• a very young age or very low body weight.

It is also worth reviewing whether the dog genuinely needs every active ingredient contained in a combination product.

If a dog develops a new symptom after a parasite-control product

If, after using a product, the dog develops:

• tremor;
• loss of balance or coordination;
• a seizure;
• marked lethargy;
• repeated vomiting or diarrhoea;
• a severe skin reaction;
• difficulty breathing;
• swelling of the face or throat;
• or any other unexpected symptom,

contact a veterinarian.

Always tell the veterinarian:

• which parasite-control product was used;
• the date it was given or applied;
• which dose in the series it was;
• and when the symptoms began.

This also applies if a longer period has passed since the medicine was administered.

It is also worth reporting a suspected adverse effect to the pharmacovigilance system.

Spontaneous adverse-event reports cannot by themselves be used to calculate the true incidence of an adverse effect, but they are very important for detecting rare or delayed safety signals.

Summary

After external parasites, internal parasites, collars, spot-ons, tablets, combination products and long-acting injections, the whole subject can be summarised surprisingly simply: parasite control is not one universal ‘protection’, but risk management. First identify which parasite you actually need protection from, and only then choose the most justified active substance or other measure.

A tick-control product can reduce the risk of ticks and tick-borne disease. At the same time, every pharmacologically active product can have adverse effects.

No product guarantees that a dog will never pick up a tick or never become infected with a tick-borne disease. The goal should therefore not be ‘the strongest possible product’.

A more useful goal is sufficient protection for this particular dog’s actual level of risk, using the most informed choice possible.

For one dog, the most realistic problem may be ticks; for another, Dipylidium brought home through fleas; for a third, prey-borne tapeworm risk associated with hunting; and for a fourth, Dirofilaria related to travel or mosquitoes. The ‘broadest-spectrum’ product is therefore not automatically the most informed choice.

In practice, this often means combining several small risk-reduction measures:

• choosing a suitable product or repellent;
• regular tick checks;
• removing ticks that are still moving in the coat;
• prompt removal of attached ticks;
• taking the individual dog’s health background into account;
• and avoiding active ingredients that are not needed.

In the end, the most important question is not ‘Which tick treatment is the most powerful?’ but ‘Which approach is justified for this particular dog?’

Main sources

• European Union veterinary medicines database / Union Product Database: current product information for the medicines discussed.
• European Medicines Agency: veterinary medicine assessment and pharmacovigilance materials.
• U.S. Food and Drug Administration: Fact Sheet for Pet Owners and Veterinarians about Potential Adverse Events Associated with Isoxazoline Flea and Tick Products.
• ESCCAP: tick-control guidance and recommendations for regular tick checks.
• Bates N, Dijkman MA, Edwards JN. Neurological adverse effects of isoxazoline exposure in cats and dogs. Veterinary Record, 2024.
• Molaba GG et al. A systematic literature review of the efficacy of acaricidal plants, plant extracts, and tick assays used against dog-associated ticks. Acta Tropica, 2025.
• Merck Veterinary Manual. Toxicoses From Essential Oils in Animals, updated 2025.
• Merck Veterinary Manual. Garlic and Onion (Allium spp) Toxicosis in Animals, 2024.
• Junnila A et al. Efficacy of repellents against fleas and ticks: a field trial on free roaming dogs in Mali, West Africa. Frontiers in Insect Science, 2026. doi:10.3389/finsc.2026.1811490.
• ESCCAP. GL1 / MG1: Worm Control in Dogs and Cats, 2026; individual risk assessment for worm control and the main European helminths.
• ESCCAP. GL3: Control of Ectoparasites in Dogs and Cats, 2024; fleas, ticks, lice and mites.
• ESCCAP. GL6: Control of Intestinal Protozoa in Dogs and Cats, 2025; Giardia and other intestinal protozoa.
• Mõttus M, Mõtsküla PF, Jokelainen P. Heartworm disease in domestic dogs in Estonia: indication of local circulation of Dirofilaria immitis farther north than previously reported. Parasites & Vectors. 2024;17:124.
• Mõtsküla M, Mõtsküla PF, Saarma U. First molecularly confirmed Angiostrongylus vasorum infection in a dog in Estonia: translocation risks and diagnostic pitfalls. Journal of Helminthology. 2026.
• Laurimaa L et al. Echinococcus multilocularis and other zoonotic parasites in red foxes in Estonia. Parasitology. 2016;143:1450–1458.
• Washington State University / WADDL. MDR1 in Dogs; ABCB1/MDR1 variant, breeds at risk and drug-safety information.
• European Medicines Agency. QRD veterinary product-information template: definitions of adverse-effect frequency categories.
• CDC Healthy Pets, Healthy People (2026): zoonoses, hand hygiene and family members at increased risk.
• Current product information/package leaflets for the products discussed: user safety, child exposure, bed-sharing warnings, NMP, hypersensitivity and respiratory precautions for sprays.
• Nchu F, Magano SR, Eloff JN. Repellent activities of dichloromethane extract of Allium sativum (garlic) against Hyalomma rufipes. Journal of the South African Veterinary Association. 2016;87(1):1356. doi:10.4102/jsava.v87i1.1356.
• Buckley LA. Can garlic prevent, repel or kill fleas that infest dogs? Veterinary Evidence. 2020;5(3). doi:10.18849/ve.v5i3.311.
• Barrett M, DVM. ‘Natural Flea & Tick Control’. Holistic Dog Care Summit 2.0, Pet Summits, 2024; FendaF notes from the presentation. Pet Summits course archive.
• European Medicines Agency. Guideline for the testing and evaluation of the efficacy of antiparasitic substances for the treatment and prevention of tick and flea infestation in dogs and cats, Rev. 4.
• Estonian State Agency of Medicines. Medicinal waste: instructions for sorting and returning medicinal waste, 2026.

 

 

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