Ivermectin

22,23-dihydroavermectin B1a + 22,23-dihydroavermectin B1b

Antiparasitic - Macrocyclic Lactone (Avermectin)POSCIMTopicalDogsCatsSmall MammalsFerretsBirdsReptilesHorsesCattleSwineSheepGoats

Also known as: Heartgard · Ivomec · Equimectrin · Eqvalan · Zimectrin · Equimax · Phoenectin · Tri-Heart Plus · Panacur Plus · Stromectol · Otimectin Vet · Panomec · MK 933 · Ivermectine · Ivermectinum · Ivermectina

Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference

6-12 micrograms/kg PO once monthlyPO· once monthly

Body weight— 🐕

Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.

Dosing by species

🌎 NA — North America🌍 EU — Europe

Dogs

Indication	Dose	Route	Frequency	Duration	Region
As a preventative for heartworm	6-12 micrograms/kg PO once monthly	PO	once monthly	—	🌎 NA
As a preventative for heartworm	Minimum dosage of 6 micrograms/kg (0.006 mg/kg) PO per month.	PO	per month	—	🌎 NA
As a microfilaricide	6-12 micro-grams/kg PO once a month	PO	once a month	—	🌎 NA
As an adulticide or pre-adulticide for heartworm (with doxycycline)	6-14 micrograms/kg PO once every 15 days for 6 months	PO	once every 15 days	6 months	🌎 NA
For generalized demodicosis	Day 1: 100 micrograms/kg PO q24h, Day 4: 200 micrograms/kg PO q24h, Day 7: 300 micrograms/kg; continue to increase by 100 micro-grams/kg every 3rd day until reach target dose of 600 micrograms/kg PO daily	PO	q24h	1-2 months after 2 negative skin scrapes	🌎 NA
For demodicosis (alternative protocol)	Start at a trial dose of 0.05 mg/kg (50 micrograms/kg) day 1. Then increase the dose to 0.12 mg/kg for the next week... go up to 0.2 mg/kg for the next 3 days, and then increase the dose weekly by 0.1 mg/kg until you reach 0.6 mg/kg.	PO	daily	2 months past negative scrapings	🌎 NA
As scabicide	300-400 micrograms/kg PO or SC once weekly for weeks.	PO/SC	once weekly	for weeks	🌎 NA
For treatment of parasitic lung disease (Capillaria spp.)	0.2 mg/kg PO once	PO	once	—	🌎 NA
For Oslerus osleri	0.4 mg/kg SC once	SC	once	—	🌎 NA
For Eucoleus boehmi	0.2 mg/kg PO once	PO	once	—	🌎 NA
For Pneumonyssoides caninum	0.2 mg/kg SC once	SC	once	—	🌎 NA

As a microfilaricide: To kill third, fourth, and young fifth stage larvae. Alternatively, 50 micrograms/kg for rapid kill (higher risk of adverse effects).
As an adulticide or pre-adulticide for heartworm (with doxycycline): Used in combination with doxycycline 10 mg/kg PO once daily for 30 days.
For generalized demodicosis: Do not use in ABCB1-1Δ susceptible breeds unless tested normal/normal.
As scabicide: Beware in sensitive breeds.

Cats

Indication	Dose	Route	Frequency	Duration	Region
As a preventative for heartworm	0.024 mg/kg (24 micrograms/kg) PO every 30-45 days	PO	every 30-45 days	—	🌎 NA
For Aelurostrongylus abstrusus	0.4 mg/kg SC once	SC	once	—	🌎 NA
Ear mites	1 mg/g ear gel	topical	Not specified	Not specified	🌍 EU

As a preventative for heartworm: Also controls hookworms at this dosage.
Ear mites: Otimectin Vet. Do not use in kittens under 16 weeks.

Small Mammals

Indication	Dose	Route	Frequency	Duration	Region
Rabbits: For Sarcoptes scabiei, Notoedres cati	0.3-0.4 mg/kg SC, repeat in 14 days.	SC	repeat in 14 days	—	🌎 NA
Rabbits: For ear mites (Psoroptes)	0.2-0.44 mg/kg PO, SC repeat in 8-18 days	PO/SC	repeat in 8-18 days	—	🌎 NA
Rabbits: For treatment of ear mites	200 micrograms/kg SC and repeated in two weeks.	SC	repeated in two weeks	—	🌎 NA
Rodents and lagomorphs: For treatment of sarcoptoid and some fur mites	200-250 micrograms/kg SC.	SC	once	—	🌎 NA
Mice, Rats, Gerbils, Guinea pigs, Chinchillas	200 micrograms/kg SC or PO every 7 days for 3 weeks	SC/PO	every 7 days	3 weeks	🌎 NA
Hamsters	200-500 micrograms/kg SC or PO every 14 days for 3 weeks	SC/PO	every 14 days	3 weeks	🌎 NA
Guinea pigs for Trixacarus caviae mites	500 micrograms/kg SC, repeated at 14 and 28 days.	SC	repeated at 14 and 28 days	—	🌎 NA

Rabbits: For treatment of ear mites: All rabbits in colony should be treated.

Ferrets

Indication	Dose	Route	Frequency	Duration	Region
For prevention of heartworm disease	0.02 mg/kg PO monthly	PO	monthly	—	🌎 NA
To treat heartworm disease using the very slow protocol	50 micrograms PO once a month.	PO	once a month	—	🌎 NA

Birds

Indication	Dose	Route	Frequency	Duration	Region
For ascarids, Capillaria, Knemidocoptes pilae	Inject 220 micrograms/kg IM; Amazons: 0.1 mg IM; Macaws: 0.2 mg IM; Finches: 0.02 mg	IM	once	—	🌎 NA
For most species	200 micrograms/kg IM or orally; repeat in 10-14 days.	IM/PO	repeat in 10-14 days	—	🌎 NA
Budgerigars	0.01 mL of diluted product (see above) IM or PO	IM/PO	once	—	🌎 NA
For most species	200 micrograms/kg (0.2 mg/kg) SC; dilute using propylene glycol.	SC	once	—	🌎 NA
Ratites	200 micrograms/kg PO, IM or SC.	PO/IM/SC	once	—	🌎 NA

For ascarids, Capillaria, Knemidocoptes pilae: Dilute to a 2 mg/mL concentration or dilute bovine prep 1:4 with propylene glycol.
Ratites: Has efficacy against Chandlerella quiscali in emus.

Reptiles

Indication	Dose	Route	Frequency	Duration	Region
For most nematodes, ectoparasites (Lizards, snakes, alligators)	0.2 mg/kg (200 micrograms/kg) IM, SC, or PO once; repeat in 2 weeks.	IM/SC/PO	repeat in 2 weeks	—	🌎 NA

For most nematodes, ectoparasites (Lizards, snakes, alligators): A third treatment can be given if still positive. Toxic to chelonians, indigo snakes, skinks.

Horses

Indication	Dose	Route	Frequency	Duration	Region
For susceptible parasites	200 micrograms/kg (0.2 mg/kg) PO using oral paste or oral liquid	PO	once	—	🌎 NA
For lice and mange	0.2 mg/kg PO; 0.2 mg/kg PO at 4 day intervals	PO	at 4 day intervals	—	🌎 NA
As a larvicidal for arterial stages of S. vulgaris	0.2 mg/kg once	PO	once	—	🌎 NA

Cattle

Indication	Dose	Route	Frequency	Duration	Region
For susceptible parasites	200 micrograms/kg SC.	SC	once	—	🌎 NA
For psoroptic mange	200 mg/kg IM	IM	once	—	🌎 NA
For susceptible parasites	200 micrograms/kg (0.2 mg/kg) SC under the loose skin in front of or behind the shoulder	SC	once	—	🌎 NA

For susceptible parasites: Doses greater than 10 mL should be given at two separate sites.
For psoroptic mange: Note: Reference was written before approval of the SC labeled bovine product; isolate from other cattle for at least 5 days after treatment.

Swine

Indication	Dose	Route	Frequency	Duration	Region
For susceptible parasites	300 micrograms/kg (0.3 mg/kg) SC in the neck immediately behind the ear	SC	once	—	🌎 NA
For general control of endo- and ectoparasites in potbellied pigs	300 micro-grams/kg SC or IM once for internal parasites and repeated in 10-14 days for external parasites	SC/IM	once, repeat in 10-14 days	—	🌎 NA

For general control of endo- and ectoparasites in potbellied pigs: Only partially effective against whipworms.

Sheep

Indication	Dose	Route	Frequency	Duration	Region
For nasal bot infection	200 micrograms/kg	SC/PO	once	—	🌎 NA
For susceptible parasites	200 micrograms/kg SC for one dose	SC	once	—	🌎 NA
For adjunctive treatment of meningeal worm (Parelaphostrongylus tenuis)	0.3 mg/kg SC once daily for 5 days	SC	once daily	5 days	🌎 NA
Camelids: For susceptible parasites	0.2 mg/kg PO or SC for one dose	PO/SC	once	—	🌎 NA
Camelids: For GI helminths	0.2 mg/kg PO once.	PO	once	—	🌎 NA
Camelids: For adjunctive treatment of meningeal worm	0.3 mg/kg SC once daily for 5 days.	SC	once daily	5 days	🌎 NA

For adjunctive treatment of meningeal worm (Parelaphostrongylus tenuis): Given with fenbendazole (50 mg/kg PO once daily for 5 days).
Camelids: For adjunctive treatment of meningeal worm: Given with fenbendazole. Camelids very susceptible to GI ulcers; give prophylaxis.

Goats

Indication	Dose	Route	Frequency	Duration	Region
For susceptible parasites	200 micrograms/kg SC for one dose	SC	once	—	🌎 NA

Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.

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Overview

Ivermectin is a prototype avermectin antiparasitic agent widely used across multiple veterinary species. It is a macrocyclic lactone derivative highly effective against a broad spectrum of nematodes and arthropods.

Key Clinical Highlights:

FDA-Approved Uses: Heartworm prevention in dogs and cats; treatment of gastrointestinal roundworms, lungworms, grubs, lice, and mites in cattle, swine, horses, reindeer, and bison.
Extra-Label Uses: Microfilaricide, slow-kill adulticide (often combined with doxycycline), and treatment for generalized demodicosis and scabies in small animals.
Genetic Sensitivity: Extreme caution is required in breeds susceptible to the ABCB1-1Δ (formerly MDR1) mutation (e.g., Collies, Australian Shepherds, Shetland Sheepdogs, Long-haired Whippets). These dogs lack a functional P-glycoprotein pump at the blood-brain barrier, leading to severe, potentially fatal CNS toxicity at doses commonly used for mange or microfilariae.
Toxicity Profile: Generally safe at low heartworm preventative doses (even in MDR1 dogs), but neurotoxicity risk increases significantly at higher doses or when combined with P-glycoprotein inhibitors.

Mechanism of action

Ivermectin exerts its antiparasitic effect by binding selectively and with high affinity to glutamate-gated chloride channels which occur in invertebrate nerve and muscle cells.

Primary Mechanism: Binds to glutamate-gated chloride channels → increases cell membrane permeability to chloride ions → hyperpolarization of the nerve or muscle cell → flaccid paralysis and death of the parasite.
Secondary Mechanism: Enhances the release of gamma-aminobutyric acid (GABA) at presynaptic neurons. GABA acts as an inhibitory neurotransmitter → blocks post-synaptic stimulation → paralysis.

Pharmacology Pearl: Because flukes (trematodes) and tapeworms (cestodes) do not utilize GABA as a peripheral nerve transmitter and lack glutamate-gated chloride channels, ivermectin is completely ineffective against these parasites. Mammals generally lack glutamate-gated chloride channels, and mammalian GABA receptors are confined to the CNS, which ivermectin does not readily cross (unless the P-glycoprotein pump is defective or overwhelmed), providing a wide margin of safety.

Safety & warnings

Contraindications

Foals less than 4 months old (manufacturer recommendation)
Puppies less than 6 weeks old
Breeds susceptible to ABCB1-1Δ (MDR1) mutation at high doses (unless tested normal)
Chelonians (turtles, tortoises)
Indigo snakes
Skinks
Lactating dairy animals (no milk withdrawal established)
Females of breeding age (cattle/swine, per label)
Dogs with the MDR1 (ABCB1) gene mutation (unless using strictly at low heartworm preventative doses)
Chelonians (turtles and tortoises) - causes fatal flaccid paralysis
Kittens under 16 weeks of age (for topical ear gel)
Use of concentrated livestock formulations in small animals

Adverse effects

Horses: Ventral midline swelling and pruritus (hypersensitivity to dying Onchocerca microfilariae)
Dogs: Shock-like reaction (when used as microfilaricide), depression, hypothermia, vomiting
Dogs (MDR1/Toxicity): Ataxia, lethargy, hypersalivation, mydriasis, tremors, seizures, blindness, coma
Cats: Agitation, vocalization, anorexia, mydriasis, rear limb paresis, tremors, disorientation, blindness
Cattle: Paralysis/staggering or salivation/bloat (if Hypoderma bovis larvae are killed in vital areas), injection site swelling
Birds: Lethargy, anorexia, death (especially in finches and budgerigars)
Neurotoxicity (ataxia, tremors, mydriasis, blindness, coma, death) - especially in MDR1-mutant dogs
Bradycardia

Precautions

MDR1 Gene Mutation Warning: Ivermectin is actively transported out of the CNS by the P-glycoprotein pump. Dogs with the ABCB1-1Δ (formerly MDR1) mutation have a defective pump, allowing ivermectin to accumulate in the brain, causing severe neurotoxicity. Always test susceptible breeds (Collies, Shelties, Australian Shepherds, Long-haired Whippets, 'white feet' breeds) before using extra-label high doses. Heartworm preventative doses are generally safe.

Species Sensitivities: Highly toxic to chelonians (turtles/tortoises), indigo snakes, and skinks. Finches and budgerigars are highly sensitive.
Cattle Grubs: Treating cattle for Hypoderma bovis when larvae are migrating through the spinal canal or esophagus can cause severe host reactions (paralysis or bloat) due to larval death in vital areas.
Food Animal Withdrawal: Strict adherence to slaughter withdrawal times is required. Not approved for lactating dairy animals.
Administration: Injectable products for cattle and swine are for SC use only; do not administer IM or IV.

Drug interactions

Benzodiazepines

Effects may be potentiated by ivermectin; concurrent use is not advised.

Ketamine

Avoid ivermectin in reptiles within 10 days of ketamine administration.

SpinosadMajor

Increased risk of neurotoxicity; do not use with high extra-label doses of ivermectin.

Amiodarone