# Ivermectin Paste: Uses, Dosing and Safety Ivermectin paste is an oral deworming product formulated and labeled for horses. The familiar product in this category is the 1.87% equine oral paste, packaged in a calibrated syringe that delivers the drug at roughly 200 micrograms per kilogram of body weight when the plunger is set to the horse's weight [1]. It is an over-the-counter livestock and equine product in the United States, which is precisely why it ends up in the hands of pet owners who want a cheap wormer. Used as labeled in a horse, it is a well-tolerated and highly effective anthelmintic. Used off-label in a dog, cat, or exotic pet without veterinary supervision, it can cause serious neurologic poisoning, especially in breeds with the MDR1 (ABCB1) [gene mutation](/blog/guides/gene-mutation). This guide explains what the paste is, which parasites it does and does not kill, how the weight-calibrated dosing system works, how toxicity unfolds, and why species matters more than dose alone. > **This article is educational and is not a substitute for veterinary diagnosis or treatment.** ## At a Glance | Feature | Detail | |, - |, - | | Active ingredient | Ivermectin, typically 1.87% oral paste for horses [1] | | Drug class | Macrocyclic lactone (avermectin) endectocide | | Labeled species | Horses (equine paste formulation) | | Label dose | Approximately 200 µg/kg body weight (0.2 mg/kg) [2][3][1] | | How it is given | Oral paste deposited on the back of the tongue, dosed by a calibrated plunger marked in body weight | | Onset of parasite kill | Fecal egg reduction is measurable by roughly day 7 to 14 after treatment [1][4] | | Duration of effect | Egg suppression commonly persists several weeks, with strongyle egg counts staying low for 8 to 10 weeks in study settings [5][1][6] | | Legal status in the US | Over-the-counter equine/livestock product. Not approved for dogs, cats, or exotic pets | | Fleas and ticks | Not a flea or tick product when given orally to horses | | Tapeworms and flukes | Not covered by ivermectin alone [7] | ## What Ivermectin Paste Is The equine paste is a thick, flavored gel supplied in a plastic syringe with a ring or dial on the plunger. The barrel is printed with weight graduations. You set the ring to the horse's weight, lock the syringe at the corner of the mouth, and depress the plunger to deposit the paste on the tongue. This design is why the paste is popular: it allows precision in dosage compared with powders or granules added to feed, and it is convenient to administer [8]. That same convenience is a hazard. The product is calibrated for animals weighing hundreds of kilograms. A single graduation mark intended for a 250 kg foal may deliver a dose that is enormous relative to a 10 kg dog. Ivermectin has a wide margin of safety in horses and in most dogs at appropriate antiparasitic doses, but the margin is not infinite, and the toxic threshold drops sharply in animals with a defective blood-brain barrier transporter. ### Why It Is Formulated for Horses The 1.87% concentration is a horse-specific formulation choice. Comparative work has shown that ivermectin delivered as the 1.87% equine paste at 200 µg/kg produces strongyle egg reductions of 100% at posttreatment days 14, 28, and 56, with reductions of 93.4% to 98.7% at day 70 [1]. No adverse reactions to treatment were observed in that study. A separate controlled trial in ponies found the oral paste formulation was greater than 98% effective against several internal parasites at the same 0.2 mg/kg dose [7]. The paste is not the only way to give ivermectin to a horse. A liquid drench formulation given by nasogastric tube at 200 µg/kg produced no signs of toxicosis and suppressed strongyle eggs for up to 8 weeks in treated horses [9]. The choice between paste, drench, and injectable comes down to convenience, owner skill, and veterinarian preference, not to a difference in the drug itself. ## How Ivermectin Works Ivermectin belongs to the macrocyclic lactone family. It opens glutamate-gated chloride channels in the nervous system and muscle of susceptible parasites. The resulting influx of chloride ions hyperpolarizes the parasite's cells, paralyzes the worm, and leads to its death or expulsion. Mammals are largely protected from this effect because their glutamate-gated chloride channels are not as accessible to the drug, and because a membrane transporter called P-glycoprotein, encoded by the ABCB1 (formerly MDR1) gene, actively pumps ivermectin out of the central nervous system. That transporter is the single most important safety concept in this entire article. When P-glycoprotein works normally, the brain is protected from the drug. When it is defective or overwhelmed, ivermectin accumulates in the central nervous system and produces the classic neurotoxic syndrome. ### Absorption and Persistence in Horses Ivermectin absorption after oral paste dosing is not instantaneous. In one pharmacokinetic study, peak plasma concentrations in mares occurred 2 to 24 hours after spring treatment and 2 to 36 hours after autumn treatment, and absorption was significantly slower in autumn than in spring [10]. Peak plasma concentrations across individual horses ranged widely, roughly 6 to 43 ng/mL depending on the season and animal. The drug persists long enough to suppress egg shedding for weeks. In a study comparing routes of administration, the equine paste at 0.2 mg/kg reduced fecal strongyle egg counts by more than 95% for 10 weeks, while a pour-on formulation at 0.5 mg/kg produced a lower and more variable reduction of 82% to 97% [6]. Another study found oral ivermectin reduced egg counts by 96% to 100% for up to 8 weeks [5]. Formulation and route genuinely change drug behavior. A study in reindeer calves compared oral liquid drench, oral paste, and subcutaneous injection, all at 200 µg/kg. Peak plasma concentration was 30.2 ng/mL for the oral liquid, 14.9 ng/mL for the oral paste, and 63.1 ng/mL for the injection [11]. The paste produced the lowest systemic exposure of the three. This is a useful reminder that "the same dose" does not mean "the same blood level" across formulations and species. ## What Ivermectin Paste Treats ### Labeled Parasite Coverage in Horses Ivermectin paste at 200 µg/kg is effective against a broad range of equine nematodes and bots. Controlled and field studies document efficacy against: - **Large strongyles** including *Strongylus vulgaris* and *S. edentatus*, with efficacy at or near 100% [12][7] - **Small strongyles (cyathostomins)**, with egg count reductions typically above 95% for weeks after treatment [5][6] - **Ascarids (*Parascaris equorum*)**, including adult stages at 100% efficacy and larval stages at 91% to 93% efficacy in foals [2][3] - **Pinworms (*[Oxyuris equi](/knowledge/parasites/livestock-parasites/oxyuris-equi-horse-pinworm-pruritus-ani-perianal-egg-deposits)*)**, with 100% efficacy against larvae in the paste formulation [7] - **Bots (*[Gasterophilus intestinalis](/knowledge/parasites/livestock-parasites/gasterophilus-intestinalis-equine-bot-fly-larvae-stomach-walls-control)* and *G. nasalis*)**, with efficacy greater than 98% [7] - ***[Trichostrongylus axei](/knowledge/parasites/livestock-parasites/trichostrongylus-axei-abomasal-hairworm)*, *Habronema* species, and *Triodontophorus* species** [12][7] - **Onchocerca microfilariae** in the skin, though not the adult worms [13] ### Onchocerciasis and Skin Disease A classic study treated 12 horses with ivermectin paste. Skin microfilariae of *Onchocerca cervicalis* were present in biopsies before treatment and absent from all biopsies one week after treatment [13]. Skin lesions regressed within 7 days and affected skin returned to normal within 3 months. Microfilariae began to reappear in some horses about 2 months after treatment, which means the drug controls the microfilarial stage but does not eliminate the adult worm. Eight of the horses developed transient skin reactions 4 to 24 hours after dosing, including weals over the neck, shoulders, and flanks, plus pitting edema along the ventral midline. These reactions reflect the dying microfilariae, not an allergy to the paste itself. Notably, the paste did not improve lesions of Queensland itch in that study, which reinforces that ivermectin treats what it treats and nothing more [13]. ## What Ivermectin Paste Does Not Treat This is where owners most often go wrong. **Tapeworms.** Ivermectin alone does not kill equine tapeworms (*Anoplocephala* species). In a controlled pony study, the drug was effective against a long list of parasites "except Anoplocephala spp." [7]. Tapeworm control requires a different drug. Praziquantel paste at 1 mg/kg reduced cestode eggs by more than 99% in donkeys for up to 16 weeks, and it was the praziquantel component, not the ivermectin given alongside it, that did that work [14]. Combination products containing both ivermectin and praziquantel are available and have shown strong combined efficacy against nematodes and cestodes [15]. **Flukes.** Ivermectin is not a flukicide. It has no established role in treating liver flukes in horses, and no source in this review supports its use for that purpose. **Fleas, ticks, and environmental parasites.** The equine oral paste is not a flea or tick control product. Do not assume that because ivermectin kills some external parasites in some species, the horse paste will solve a flea problem in a dog or cat. **Adult *Onchocerca* worms.** As noted above, the paste controls microfilariae but does not eliminate adult worms, which is why skin microfilariae can reappear about 2 months after treatment [13]. ## Dosing the Equine Paste Read this section as a description of label dosing for horses, not as a dosing guide for any other species. ### The 200 µg/kg Standard The standard equine dose is 0.2 mg/kg, which is 200 micrograms per kilogram of body weight [2][3][1][16]. The 1.87% paste syringe is built around this number. You estimate or measure the horse's weight, set the plunger's calibration ring to that weight, and deliver the corresponding volume. A girth tape is commonly used to estimate body weight in the field [4]. ### Why the Weight Calibration Matters Underdosing is the quiet failure mode. If you guess the weight low, you leave worms alive and select for resistant parasites. Overdosing is the loud failure mode, though the horse's tolerance is broad and appropriate dosing rarely causes toxicity on its own. One important field observation: in a herd outbreak of neurologic signs after ivermectin administration, serum ivermectin concentrations were higher than expected for the dose given, and the administration tubes themselves did not contain excess drug [17]. The hay was heavily contaminated with two *Solanum* species. The lesson is that a horse can show ivermectin toxicity after a correct dose if it is simultaneously eating a toxic plant. Plant exposure and drug exposure can compound. ### Dosing Frequency and Rotation Frequency is a herd-health decision, not a fixed rule. Repeated exclusive use of ivermectin over many years has been associated with reduced activity against small strongyles on at least one farm. In field studies on a Central Kentucky farm where horses received ivermectin almost exclusively four times a year since 1990, researchers documented reduced activity of ivermectin against small strongyles [4]. This is the practical argument for fecal egg count monitoring and for discussing a rotation or combination strategy with a veterinarian rather than deworming on a calendar. ## Species Cautions: This Is Not a Dog or Cat Dewormer The single most important sentence in this article: the equine paste is formulated for horses, and it should not be used off-label in dogs, cats, or exotic pets without explicit veterinary guidance. The reason is not that ivermectin is uniquely dangerous. It is that the safety margin depends on species, breed, age, body weight, and formulation, and the paste removes the safeguards. There is no weight graduation on an equine paste syringe for a 5 kg cat. ### The MDR1 (ABCB1) Mutation Certain dog breeds carry a mutation in the ABCB1 gene that disables P-glycoprotein, the transporter that keeps ivermectin out of the brain. In these dogs, a dose that would be harmless to a normal dog can produce severe neurotoxicity. Collies and related herding breeds are the classic examples. If you own a dog of a breed known to carry this mutation, or a mixed breed with herding ancestry, treat any ivermectin exposure as an emergency and call a veterinarian or pet poison control immediately. Never give an equine ivermectin paste to a dog of any breed without a veterinarian's explicit instruction, and never to a dog with a known or suspected MDR1 mutation at any dose. ### Young Animals Neonates and very young animals are more vulnerable to ivermectin neurotoxicity because the blood-brain barrier is still maturing. This is a general principle of neurotoxic drug exposure and it applies here. Do not extrapolate a horse dose down to a puppy, kitten, or juvenile exotic pet. ### Species Table | Species | Approved formulation | Key caution | |, - |, - |, - | | Horse | Ivermectin 1.87% oral paste (equine) | Label dose 200 µg/kg. Estimate weight accurately and set the plunger to that weight [1][4]. Do not use ivermectin alone where tapeworm coverage is needed [7]. | | Dog | None in this category (equine paste is not approved for dogs) | Off-label use only under veterinary direction. High risk of neurotoxicity in MDR1/ABCB1-mutant breeds. Never dose from a horse syringe by guesswork. | | Cat | None in this category | Off-label use only under veterinary direction. Small body size makes paste dosing errors large in relative terms. | | Exotic pets and small mammals | None in this category | Off-label use only under veterinary direction. Do not scale a horse dose to a rabbit, guinea pig, or bird. | If your pet needs deworming, the correct answer is a product approved for that species, prescribed at a weight-appropriate dose by a veterinarian, not a syringe designed for a 500 kg animal. ## Side Effects and What to Do About Them ### Expected Reactions in Horses Transient skin reactions can occur when microfilariae die. In the onchocerciasis study, 8 of 12 treated horses developed weals and pitting edema 4 to 24 hours after dosing, and these reactions resolved [13]. This is a treatment effect, not an intolerance. Mild, transient softening of feces has also been reported with paste dewormers in horses [18]. ### Neurotoxicity: The Serious Syndrome Ivermectin toxicity is a neurologic syndrome. The signs progress in a recognizable order: 1. **Mydriasis** (dilated pupils) and visual disturbance 2. **Ataxia** (incoordination, stumbling, swaying) 3. **Tremors** and muscle fasciculations 4. **Depression, disorientation, or altered mentation** 5. **Recumbency and coma** in severe cases A published case series described a herd of horses with acute neurologic signs after ivermectin administration, where serum ivermectin concentrations were higher than expected for the dose, and the animals were also consuming *Solanum*-contaminated hay [17]. All affected horses returned to normal neurologic function with supportive care. That outcome is encouraging but not guaranteed, and it depended on prompt veterinary involvement and intensive nursing. ### What to Do If You Suspect Toxicity If a horse, dog, cat, or other animal shows dilated pupils, wobbling, tremors, or collapse after ivermectin exposure: - **Stop giving the product immediately.** - **Call a veterinarian or an animal poison control service right away.** Do not wait to see if signs worsen. - **Bring the product packaging**, including the tube and the plunger setting, so the veterinarian can estimate the dose delivered. - **Report any possible plant exposure**, including hay or pasture, because concurrent toxic plant ingestion can amplify the effect [17]. - **Do not attempt home remedies.** There is no household antidote. Treatment is supportive and must be directed by a veterinarian. Recovery is possible with aggressive care, but the window matters. ## Who Should Not Receive Ivermectin Paste In the equine label context, use caution or avoid the product in: - **Foals below the label's minimum age or weight.** Follow the label. - **Horses with known hypersensitivity** to ivermectin or other macrocyclic lactones. - **Horses concurrently grazing or eating hay contaminated with toxic plants**, particularly *Solanum* species, because combined exposure has been linked to elevated serum ivermectin concentrations and neurologic signs after appropriate dosing [17]. - **Horses where tapeworm or fluke coverage is required**, because ivermectin alone will not do that job [7]. In the off-label pet context: - **Any dog with a known or suspected MDR1/ABCB1 mutation.** This is an absolute caution. - **Puppies, kittens, and juvenile exotic pets.** - **Any pet whose owner has not consulted a veterinarian about species-appropriate dosing.** ## Drug Interactions and Compounding Risk The most important interaction documented in this review is not a drug-drug interaction at all. It is the interaction between ivermectin and hepatically or neurologically active plant toxins. Horses given a correct dose of ivermectin still developed neurologic signs when they were simultaneously consuming *Solanum* species in hay [17]. Beyond that, the general principle is that any drug or compound that competes for P-glycoprotein transport, or that impairs liver metabolism, can raise ivermectin exposure. This is one reason off-label use in dogs is risky. Many heartworm preventives and other medications are already on board in a typical pet, and the veterinarian needs the full medication list to judge safety. Do not stack an equine dewormer on top of a pet's existing parasite prevention without professional guidance. ## How Ivermectin Paste Compares With Alternatives ### Within Equine Deworming Ivermectin paste is one option among several. Moxidectin gel at 0.4 mg/kg and ivermectin paste at 0.2 mg/kg both reduced fecal egg counts from a mean of 1600 to 0 by days 5, 7, and 14, with 100% efficacy against several shared nematode species in a Brazilian equine study [12]. The two drugs are related and their spectra overlap substantially. Praziquantel paste at 1 mg/kg covers tapeworms, which ivermectin does not [14]. A combination ivermectin plus praziquantel paste reduced strongylid and cestode egg counts by 98% or more in a large field study across North America and Europe, and 95% to 96% of treated horses that were cestode-positive before treatment became cestode-negative [15]. If tapeworm coverage is needed, the combination or a separate praziquantel product is the logical choice, not doubling up on ivermectin. Route also matters. Oral paste reduced egg counts by more than 95% for 10 weeks, while a pour-on formulation at a higher dose produced only 82% to 97% reduction [6]. In another comparison, the route of administration dramatically affected ivermectin activity against small strongyles in horses [16]. ### Across Species There is no meaningful comparison to draw between an equine paste and a dog or cat dewormer, because they are different products with different approval status, different concentrations, and different dosing systems. The appropriate comparison, when a pet needs deworming, is between veterinary-approved products for that species. ## Questions to Ask Your Veterinarian Bring these to your appointment or call: 1. Does my horse actually need ivermectin right now, based on a fecal egg count? 2. Does my horse or herd need tapeworm coverage, which ivermectin will not provide? 3. Is the estimated body weight on my syringe accurate enough, and how should I measure it? 4. My horse has skin lumps or itching. Could this be onchocerciasis, and is ivermectin the right treatment? 5. My dog or cat needs deworming. What product is approved for that species, and at what dose? 6. My dog is a collie or herding breed. Should we test for the MDR1 mutation before any ivermectin exposure? 7. My horse is also eating hay from a pasture with unknown plants. Could that change the risk of treatment? 8. How often should I be deworming, and should I rotate drug classes to slow resistance? ## Limitations and When to Contact a Veterinarian This article describes general principles of equine ivermectin paste use. It cannot tell you whether your individual animal should receive the drug, at what dose, or on what schedule. Those decisions depend on the animal's weight, age, breed, health status, parasite burden, and other medications, and they must be made by a veterinarian who has examined the animal. Contact a veterinarian promptly, and treat it as urgent, if any of the following occur: - A horse, dog, cat, or other animal develops dilated pupils, wobbling, tremors, disorientation, or collapse after any ivermectin exposure. - You gave an equine paste to a dog, cat, or exotic pet, even if the animal looks normal so far. - You gave an equine paste to a dog of a breed known to carry the MDR1/ABCB1 mutation. - Your horse's neurologic signs appeared shortly after deworming, especially if the horse is also eating hay or pasture of uncertain plant content. - Your horse has skin lesions that are not improving, or that worsen, after treatment. - You are unsure whether your deworming program is actually working, particularly if fecal egg counts remain high after treatment. Do not wait for signs to worsen on their own. Early veterinary care gives the best chance of a full recovery. ## Frequently Asked Questions ### Can I give ivermectin horse paste to my dog? No, not without a veterinarian's explicit direction. The equine paste is formulated and calibrated for horses, and the syringe has no dose marking suitable for a dog's body weight. Off-label use in dogs carries a serious risk of neurologic toxicity, especially in breeds with the MDR1/ABCB1 mutation. ### What does the 1.87% on an ivermectin paste tube mean? It is the concentration of the drug in the paste. The 1.87% equine paste is designed so that the weight-calibrated plunger delivers approximately 200 µg/kg of body weight when set correctly [1]. ### What is the standard ivermectin paste dose for a horse? The standard equine dose is 0.2 mg/kg, which equals 200 micrograms per kilogram of body weight [2][3][1]. You set the syringe's calibration ring to the horse's estimated weight and depress the plunger fully. ### Does ivermectin paste kill tapeworms? No. Ivermectin alone is not effective against equine tapeworms (*Anoplocephala* species) [7]. Tapeworm control requires praziquantel or a combination product that contains it [14][15]. ### What are the first signs of ivermectin toxicity? Dilated pupils and unsteady, wobbling movement are typical early signs, followed by tremors, depression, and in severe cases recumbency and coma. These signs require immediate veterinary attention. ### Which dogs are at highest risk of ivermectin toxicity? Dogs with the MDR1 (ABCB1) gene mutation are at highest risk. This mutation is best known in collies and related herding breeds. It disables the transporter that normally keeps ivermectin out of the brain. ### How long does ivermectin paste last in a horse? Parasite egg suppression commonly lasts several weeks. In study settings, strongyle egg counts stayed reduced by more than 95% for 10 weeks after oral paste treatment [6], and reductions of up to 8 weeks were documented in a separate trial [5]. ### Can I use ivermectin paste on my cat or rabbit? No, not without veterinary direction. The equine paste is not approved for cats, rabbits, or any exotic pet, and the dosing system is built for animals weighing hundreds of kilograms, not a few kilograms or less. ## Related Articles - [Ivermectin Cat Ear Mites](/knowledge/veterinary-medicine/parasitic-diseases/ivermectin-cat-ear-mites) - [Heartgard Plus Dose: Ivermectin Pyrantel Prevention Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/heartgard-plus-dose-ivermectin-pyrantel-prevention-guide) - [Anesthesia Machine Safety Checks for Laboratory Animal Use](/knowledge/veterinary-medicine/laboratory-animal-science/anesthesia-machine-safety-checks-laboratory-animal-use) - [Prednisone for Dogs: Uses, Side Effects, and Safety Guidelines](/knowledge/veterinary-medicine/preventive-care/prednisone-for-dogs-uses-side-effects-and-safety-guidelines) - [Cockatiel Care: Air sac mite treatment ivermectin protocol](/knowledge/veterinary-medicine/exotic-small-animals/cockatiel-care-air-sac-mite-treatment-ivermectin-protocol) - [Australian Shepherd Health Problems: MDR1 Gene and Ivermectin Drug Sensitivity](/knowledge/veterinary-medicine/breed-specific-health/australian-shepherd-health-problems-mdr1-gene-and-ivermectin-drug-sensitivity) ## Sources 1. 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[Comparative plasma disposition, bioavailability and efficacy of ivermectin following oral and pour-on administrations in horses.](https://pubmed.ncbi.nlm.nih.gov/20181429/) 7. [Efficacy of injectable and oral paste formulations of ivermectin against gastrointestinal parasites in ponies.](https://pubmed.ncbi.nlm.nih.gov/6896613/) 8. [Bioavailability and bioequivalence of veterinary drug dosage forms, with particular reference to horses: an overview.](https://pubmed.ncbi.nlm.nih.gov/1433478/) 9. [Effectiveness of an ivermectin liquid formulation given by nasogastric tube against strongyles in horses.](https://pubmed.ncbi.nlm.nih.gov/17423198/) 10. [A comparison of the efficacy and pharmacokinetics of ivermectin after spring and autumn treatments against Cyathostominae in horses.](https://pubmed.ncbi.nlm.nih.gov/26172188/) 11. [The relative plasma availabilities of ivermectin in reindeer (Rangifer tarandus tarandus) following subcutaneous and two different oral formulation applications.](https://pubmed.ncbi.nlm.nih.gov/25421461/) 12. [Comparative efficacy evaluation of moxidectin gel and ivermectin paste against internal parasites of equines in Brazil.](https://pubmed.ncbi.nlm.nih.gov/9877068/) 13. [Treatment of equine onchocerciasis with ivermectin paste.](https://pubmed.ncbi.nlm.nih.gov/3755903/) 14. [Field efficacy of praziquantel oral paste against naturally acquired equine cestodes in Ethiopia.](https://pubmed.ncbi.nlm.nih.gov/23001508/) 15. [Field efficacy of ivermectin plus praziquantel oral paste against naturally acquired gastrointestinal nematodes and cestodes of horses in North America and Europe.](https://pubmed.ncbi.nlm.nih.gov/15136982/) 16. [The route of administration drastically affects ivermectin activity against small strongyles in horses.](https://pubmed.ncbi.nlm.nih.gov/28288767/) 17. [Concurrent ivermectin and Solanum spp. toxicosis in a herd of horses.](https://pubmed.ncbi.nlm.nih.gov/22947027/) 18. [Efficacy of an oxibendazole-trichlorfon paste formulation against third stage larvae of Gasterophilus intestinalis and its safety in horses.](https://pubmed.ncbi.nlm.nih.gov/3535229/)