Milbemycin

Milbemycin oxime is a macrocyclic lactone used in small-animal parasite prevention and treatment. Its principal applications are heartworm prevention and control of selected intestinal nematodes. It is also used in combination products and has an extra-label history in canine mite disease. Additional ingredients determine the broader spectrum of combination products.

Group

Macrocyclic lactone antiparasitic

Mechanism of Action

Milbemycin oxime activates parasite glutamate-gated chloride channels, increasing chloride permeability in nerve and muscle cells. Hyperpolarization suppresses normal movement and feeding, leading to paralysis and death of susceptible parasites. Activity against developing Dirofilaria immitis larvae supports heartworm prevention. Other susceptible nematodes or mites are affected according to their sensitivity and the exposure achieved.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Heartworm and intestinal nematode prevention	0.5 mg/kg	PO	Every 720 h	Every 30 days.
Demodicosis	2 mg/kg	PO	Every 24 h	Up to 120 days; Do not use in: Macrocyclic-lactone sensitivity; Reported course 60-120 days; high-dose therapy requires tolerance and parasitological monitoring.
Demodicosis staged treatment — Initial	1 mg/kg	PO	Every 24 h	Do not use in: Macrocyclic-lactone sensitivity; Continue until clinical cure before switching to the weekly stage.
Demodicosis staged treatment — Maintenance	3 mg/kg	PO	Every 168 h	Do not use in: Macrocyclic-lactone sensitivity; After clinical cure; continue until parasitological cure with negative scrapings.
Sarcoptic mange	2 mg/kg	PO	Every 168 h	Up to 35 days; Course 3-5 weeks.
Cheyletiellosis	2 mg/kg	PO	Every 168 h
Heartworm and intestinal nematode prevention	0.5–0.99 mg/kg	PO	Every 720 h	Product-specific minimum age/weight and tablet selection apply.
Microfilariae after adulticide	0.5 mg/kg	PO		About one month after melarsomine; a two-week repeat may be used before resuming monthly prevention.
Sarcoptic mange	0.75 mg/kg	PO	Every 24 h	Up to 30 days; Separate daily alternative.
Nasal-mite-associated rhinitis	1 mg/kg	PO	Every 240 h	Three treatments at 10-day intervals.
Escalating Demodex treatment	Reference only	PO		Start 1 mg/kg/day; after 30 days with minimal improvement increase to 2 mg/kg/day, and after another 30 days consider 3 mg/kg/day or an alternative. ABCB1-mutant dogs can show toxicity at 1-2.2 mg/kg/day; maintain skin-scraping and neurologic monitoring.

Cats

Use / stage	Dose	Route	Schedule	Instructions
Heartworm and intestinal nematode prevention	2 mg/kg	PO	Every 720 h	Every 30 days.
Demodicosis	1–2 mg/kg	PO	Every 24 h

Reptiles

Use / stage	Dose	Route	Schedule	Instructions
Nematodes	Reference only	PO		0.5-1 mg/kg, repeated after 2 weeks; fecal examination 14 days after the second treatment guides further doses. Chelonian tolerance is described, unlike ivermectin, but species assessment remains necessary.

Indications

Prevention of heartworm disease in dogs and cats with a corresponding product.
Treatment and control of selected intestinal roundworms, hookworms and canine whipworms.
Extra-label treatment of selected canine demodicosis or other susceptible mite infestations.
Treatment of selected canine lungworm infections, including supported Angiostrongylus vasorum protocols, with a parasite-specific regimen.
Broad parasite control with milbemycin-containing combinations, with additional activity determined by the companion ingredients.

Contraindications

High-dose use in ABCB1-sensitive animals requires particular caution.
Previous sensitivity to macrocyclic lactones

Interactions

P-glycoprotein inhibitors, including azole antifungals and cyclosporine, can increase central nervous system exposure.

Adverse effects

Hypersalivation, ataxia, visual disturbance and central depression
Severe overdose may cause coma or death

Toxicity

Stop exposure and provide respiratory and neurologic support. Prevent further absorption when appropriate; lipid-emulsion treatment may be considered in severe lipophilic-drug intoxication.

Preparations

Preparation	Form	Strength	Route
Milbemycin oxime 2.3 mg tablet	Tablet	2.3 mg / tablet	PO
Milbemycin oxime 5.75 mg tablet	Tablet	5.75 mg / tablet	PO
Milbemycin oxime 11.5 mg tablet	Tablet	11.5 mg / tablet	PO
Milbemycin oxime 23 mg tablet	Tablet	23 mg / tablet	PO

Monitoring and Administration

Establish heartworm status before preventive treatment and use fecal examinations or skin scrapings to assess other parasite responses.

Protect from light. Do not substitute concentrated livestock products for small-animal products without exact concentration and formulation assessment.

Isoxazolines are generally preferred over prolonged high-dose milbemycin for canine demodicosis.

High-dose demodicosis treatment may require months; assess skin scrapings rather than relying on clinical appearance alone.

The cited Interceptor label excludes puppies under 4 weeks or 2 lb and kittens under 6 weeks or 1.5 lb. These are presentation-specific historical minimums rather than universal limits for every milbemycin combination. Susceptible dogs should undergo ABCB1 assessment before high-dose treatment.