Ivermectin is an antiparasitic medication used in dogs for heartworm prevention, and under veterinary supervision for treatment of mange (Demodex and Sarcoptes). It must be used with extreme caution in certain breeds.

Dosage by Purpose

Heartworm prevention: 0.006 mg/kg (6 mcg/kg) once monthly.
Sarcoptic mange: 0.2–0.4 mg/kg, protocol determined by vet.
Demodectic mange: 0.3–0.6 mg/kg daily under close vet monitoring.

⚠️ Collie & Herding Breed Warning

Dogs with the MDR1 / ABCB1 gene mutation — including Collies, Shelties, Australian Shepherds, Border Collies, and related breeds — are extremely sensitive to Ivermectin. Even heartworm-prevention doses can be toxic or fatal in these dogs. Always genetic-test susceptible breeds before use.

Signs of Ivermectin Toxicity

Symptoms include dilated pupils, tremors, drooling, ataxia, blindness, coma, and death. If overdose is suspected, contact your vet or an emergency animal poison line immediately.

🦟 Antiparasitic · Avermectin

Ivermectin Dosage Calculator for Dogs

Indication-specific ivermectin dosing for dogs — covering heartworm prevention, sarcoptic mange, demodicosis, and intestinal parasites, with critical MDR1/ABCB1 gene mutation breed safety screening built in.

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MDR1/ABCB1 MUTATION WARNING — POTENTIALLY FATAL IN AFFECTED BREEDS. Collies, Shelties, Australian Shepherds, Border Collies, McNabs, English Sheepdogs, Long-haired Whippets, Silken Windhounds and crosses may carry the MDR1 (ABCB1-1Δ) deletion. These dogs cannot clear ivermectin from the CNS, causing fatal neurotoxicity at doses used for mange. GENETIC TESTING IS MANDATORY before using ivermectin off-label in these or mixed breeds. Heartgard doses (6 mcg/kg) are generally safe even in MDR1-affected dogs; high-dose protocols are NOT.

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About Ivermectin

Drug Class

Macrocyclic Lactone — Broad-Spectrum Antiparasitic

Mechanism of Action

Ivermectin enhances glutamate-gated chloride channel conductance and GABA release in invertebrates, causing irreversible paralysis and death of susceptible parasites. In mammals, GABA receptors are in the CNS but protected by the blood-brain barrier (BBB) — in MDR1/ABCB1 mutant dogs, the BBB efflux pump P-glycoprotein is non-functional, allowing ivermectin to accumulate in the CNS and cause toxicity.

Primary Uses in Dogs

Heartworm prophylaxis (6 mcg/kg monthly), demodicosis, sarcoptic mange, ear mites, intestinal strongyles. NOT routinely used at high doses in herding breeds without MDR1 testing.

Dosing Quick Reference

Indication	Dose	Frequency
Heartworm prevention	6 mcg/kg	Monthly PO
Sarcoptic mange	200–400 mcg/kg	q2 weeks SC/PO
Demodicosis	300–600 mcg/kg	q24h PO (specialist use)
Ear mites	200–400 mcg/kg	2 doses, 2 weeks apart

Common Side Effects

MDR1 mutation dogs: neurotoxicity (ataxia, tremors, coma, death) even at low doses
Lethargy and inappetence at therapeutic doses
Vomiting
Mydriasis (dilated pupils)
Salivation and disorientation

Monitoring

MDR1 genetic testing before any off-label high-dose use. Monitor for neurological signs for 24–48 hours after first dose. Serum chemistry and CBC for chronic high-dose use.

⚠️ CRITICAL: MDR1/ABCB1 mutation testing is essential before any high-dose ivermectin use in Collies, Shelties, Australian Shepherds, Border Collies, McNabs, and related herding breeds. At-risk breeds should NOT receive high-dose ivermectin protocols without confirming MDR1 status. Signs of toxicity (ataxia, tremors, drooling, coma) require emergency veterinary care.

What Is Ivermectin?

Ivermectin is a macrocyclic lactone antiparasitic derived from Streptomyces avermitilis fermentation. It acts as a positive allosteric modulator of glutamate-gated chloride channels (GluCl) and GABA-A receptors in invertebrate nerve and muscle cells, causing hyperpolarisation, paralysis, and death of parasites. In mammals, these channels are normally excluded from the CNS by the blood-brain barrier P-glycoprotein efflux pump (ABCB1/MDR1). Dogs with the MDR1 deletion lack this pump, allowing ivermectin to accumulate in the CNS and cause severe neurological toxicity.

Pharmacokinetics in Dogs

Oral bioavailability: ~95%; fat-containing food significantly increases absorption
Half-life (dogs): ~1.5–2 days; effect persists beyond plasma half-life
Peak plasma (oral): ~4 hours
Metabolism: Hepatic CYP3A4; faecal elimination (~98%)

Dose Ranges by Indication

Heartworm prevention (FDA-approved): 6–12 mcg/kg PO monthly (Heartgard, Iverhart) — safe in ALL breeds including MDR1
Microfilaricidal (post-adulticidal): 50 mcg/kg PO once (with monitoring)
Sarcoptic mange: 200–400 mcg/kg PO or SC q2 weeks × 3–4 treatments — REQUIRES MDR1 clearance
Demodicosis (generalised): 300–600 mcg/kg PO q24h — REQUIRES MDR1 clearance; off-label use
Intestinal parasites (roundworms, hookworms): 200 mcg/kg PO once
Ear mites (Otodectes): 200–300 mcg/kg SC q2 weeks × 2

MDR1/ABCB1 Breed Risk Screening

Before using ivermectin at any dose higher than standard monthly heartworm prevention (≤12 mcg/kg), the dog’s MDR1 status must be known. The Washington State University (WSU) Veterinary Clinical Pharmacology Lab offers the gold-standard MDR1 genetic test.

Breed	MDR1 Risk	Safe for HW Prevention?	Safe for High-Dose?
Rough/Smooth Collie	~70% affected	Yes (≤12 mcg/kg)	NO — test first
Shetland Sheepdog (Sheltie)	~15% affected	Yes	NO — test first
Australian Shepherd	~50% affected	Yes	NO — test first
Border Collie	~5% affected	Yes	NO — test first
English Sheepdog (OES)	Low-moderate	Yes	NO — test first
Mixed breed (unknown ancestry)	Unknown	Yes	Test mandatory
Labrador, Golden, Beagle, etc.	Negligible	Yes	Generally safe

How to Use This Calculator

Select your dog’s breed or breed category — MDR1 safety flag will appear automatically
Enter your dog’s body weight in kg or lbs
Select the indication — dose range changes significantly by use
Select the ivermectin product/concentration available
Click Calculate to see dose in mcg, mg, and mL (for liquid formulations)

🧮 Ivermectin Dose Calculator

Breed CategoryMDR1-risk breeds: high-dose use requires genetic test first

Dog’s Weight

Weight Unit

Indication

Product / Concentration

Ivermectin Dosing Result

Signs of Ivermectin Toxicity in Dogs

If a dog develops any of the following after ivermectin administration, treat as a veterinary emergency:

Mydriasis (dilated pupils), ataxia (incoordination), tremors
Hypersalivation, vomiting, lethargy progressing to stupor
Blindness (transient or prolonged), disorientation
Respiratory depression, coma — in severe cases
Onset typically within 4–12 hours of ingestion; can persist for days to weeks in MDR1-affected dogs

Treatment: No specific antidote. Supportive care: GI decontamination if early, IV fluids, physostigmine (controversial), intralipid therapy (lipid emulsion 20%) — increasing evidence of benefit for lipophilic drug toxicity.

Frequently Asked Questions

Yes — Heartgard (ivermectin 6 mcg/kg monthly) and similar heartworm preventatives at standard doses (≤12 mcg/kg) are considered safe even in MDR1-affected Collies. The dose is 25–50× below the threshold for neurological effects in MDR1-affected dogs (300+ mcg/kg). The danger arises only with high-dose ivermectin used for mange or demodicosis (200–600 mcg/kg), which is 30–100× higher than the heartworm prevention dose.

Yes, but with extreme caution — this is an off-label use. The 1% injectable solution (10 mg/mL = 10,000 mcg/mL) is sometimes administered orally to dogs for mange, but the high concentration makes accurate dosing for small dogs very difficult and errors potentially fatal. A tiny volume (e.g., 0.04 mL for a 20 kg dog at 200 mcg/kg) is prone to measurement error. Many veterinarians prefer a diluted formulation (0.08% = 800 mcg/mL) for oral use in small dogs. This should only be done under direct veterinary supervision with confirmed MDR1-negative status.

The MDR1/ABCB1 genetic test can be performed via a simple cheek swab. Reputable laboratories include: Washington State University Veterinary Clinical Pharmacology Lab (USA), Genoscoper/MyDogDNA (Europe), Orivet (Australia/global), and Embark (includes MDR1 in their breed health panel). Results are reported as Normal/Normal (++), Mutant/Normal (+/-), or Mutant/Mutant (-/-). Dogs that are +/- or -/- are at risk and should not receive high-dose ivermectin. Results are permanent — one lifetime test is sufficient.

Several effective antiparasitic alternatives do not rely on P-glycoprotein efflux and are safe in MDR1-affected dogs: Milbemycin oxime (Interceptor, Sentinel) for heartworm prevention and intestinal parasites — safe in MDR1 dogs at licensed doses; Selamectin (Revolution) — generally safe at licensed topical doses; Doramectin — similar risk profile to ivermectin, use with caution; Sarolaner, fluralaner, afoxolaner (IsoxazolineNSAID class — Simparica, Bravecto, NexGard) — safe alternatives for mite and flea/tick control. Discuss with your vet for the best alternative for your specific indication.

For generalised demodicosis in MDR1-negative dogs, ivermectin is titrated gradually to minimise toxicity risk: typically starting at 100 mcg/kg PO q24h on Day 1, increasing by 100 mcg/kg every 1–2 weeks until the target dose of 400–600 mcg/kg/day is reached. Treatment continues until two consecutive negative deep skin scrapings are obtained (typically 3–6 months). Modern isoxazoline treatments (Bravecto, NexGard, Simparica) have largely replaced ivermectin for demodicosis due to superior safety profiles and equivalent or better efficacy — discuss with a veterinary dermatologist.

References

Plumb DC. Plumb’s Veterinary Drug Handbook, 9th ed. Wiley-Blackwell; 2018.
Mealey KL, et al. Ivermectin sensitivity in collies is associated with a deletion mutation of the mdr1 gene. Pharmacogenetics. 2001;11(8):727-733.
Mealey KL. Therapeutic implications of the MDR-1 gene. J Vet Pharmacol Ther. 2004;27(4):257-264.
Papich MG. Saunders Handbook of Veterinary Drugs, 4th ed. Elsevier; 2016.
Mueller RS. Treatment protocols for demodicosis: an evidence-based review. Vet Dermatol. 2004;15(2):75-89.
Washington State University Veterinary Clinical Pharmacology Lab. MDR1 mutation testing. vetmed.wsu.edu; 2023.