Melarsomine: veterinary dose and monograph

At a glance

Drug class

Antiparasitic

Also known as

Immiticide, Diroban

Species with doses

Dogs

General dose range

2.5 mg/kg IM per adulticide protocol — check the species tables for the indication

Routes

IM

Last reviewed

1 October 2026

Indications

• Adult canine heartworm infection (stabilised, AHS adulticide protocol)

Melarsomine dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Heartworm adulticide (3-injection AHS protocol): Papich 5e: deep IM; follow American Heartworm Society guidelines — three-dose protocol with injections on days 60, 90 and 91 after diagnosis. Plumb’s p.776: 2.5 mg/kg deep IM into the lumbar epaxial muscles (L3–L5), alternating sides; the 3-injection protocol (one injection, then two 24 h apart a month later) is preferred regardless of class; label class I–II protocol is two injections 24 h apart. Low safety margin — do not confuse mg/lb with mg/kg. Strict exercise restriction; observe 24 h after the last injection.

Cats

• Not recommended: Papich 5e: melarsomine is not recommended in cats because of adverse reactions.

Contraindications

Caval syndrome (surgical worm removal needed first), very severe (class 4) heartworm disease, severe pulmonary / renal / hepatic compromise. Never give IV or SC — deep IM only.

Species-specific warnings

Cats: Not used in cats — melarsomine is too toxic for feline heartworm disease, which is managed differently.

Adverse effects

• Injection-site pain, swelling, firm nodule, sterile abscess
• Pulmonary thromboembolism (coughing, haemoptysis, collapse) as worms die
• Hepatic / renal effects; rare arsenical toxicity (managed with dimercaprol)

Drug interactions

• No major drug interactions defined; concurrent doxycycline + a macrolide is part of the modern protocol (reduces Wolbachia and worm burden / complications)
• Avoid other arsenicals and additional nephrotoxins

Pregnancy and lactation

Not for use in pregnant or breeding bitches — an arsenical with embryotoxic potential; defer adulticide therapy.

Monitoring

• Strict cage rest / leash-only from first injection until weeks after the last — the single most important survival factor
• Watch for thromboembolism: cough, dyspnoea, haemoptysis, fever, collapse
• Stage / class the heartworm disease and stabilise before adulticide

Toxicity and overdose

Arsenical toxicity causes hypersalivation, vomiting, restlessness, pulmonary oedema and hepatic / renal injury; the principal clinical danger is fatal pulmonary thromboembolism from dying worms in an exercised dog. Severe injection-site reactions occur.

Management: The specific antidote for arsenical overdose is dimercaprol (BAL). Otherwise strict cage rest, oxygen, corticosteroids and supportive care for thromboembolic / pulmonary signs; manage injection-site reactions.

Clinical pearls

• Exercise restriction is the treatment — dying worms embolise, and an excited dog can die from thromboembolism
• Use the modern 3-injection split protocol with doxycycline + a macrolide pre-treatment to reduce worm burden and complications
• Deep epaxial lumbar IM only; alternate sides for the two-injection phase and warn owners about injection-site soreness

Mechanism of action

Organic arsenical adulticide. Binds sulfhydryl groups of parasite thiol-dependent enzyme systems, killing adult Dirofilaria immitis. Worm death within the pulmonary arteries drives the thromboembolic risk that makes strict exercise restriction essential.

Formulations and products

• Immiticide / Diroban 25 mg/mL (after reconstitution)
• Immiticide (Boehringer Ingelheim) — 50 mg vial (25 mg/mL reconstituted), Deep IM injection
• Diroban (Zoetis) — 50 mg powder vial (25 mg/mL after reconstitution with 2 mL diluent — Plumb’s p.777), Deep IM injection

Storage

Store powder per label; reconstituted solution refrigerate and use within ~24 h, protected from light.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antiparasitics

• Lotilaner
• Lufenuron
• Mebendazole
• Meglumine Antimoniate
• Milbemycin oxime
• Monensin
• Monepantel
• Morantel

Frequently asked questions