# Melarsomine: veterinary dose and monograph

> Melarsomine is a veterinary antiparasitic. Organic-arsenical adulticide — the only drug approved to kill adult heartworms (Dirofilaria immitis). Indications include adult canine heartworm infection (stabilised, AHS adulticide protocol). This monograph lists 1 reference dose for dogs, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/melarsomine · Last reviewed: 2026-10-01

## 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

*Melarsomine doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Heartworm adulticide (3-injection AHS protocol) | 2.5 mg/kg | IM | one injection, then ~1 month later two injections 24 h apart | — |

- 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

*Melarsomine doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Not recommended | Not recommended in cats — adverse reactions | — | — | — |

- 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

> **Caution:** 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

> **Caution:** 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.

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## Frequently asked questions

### What is the dose of Melarsomine for dogs?

Reference doses for Melarsomine in dogs: 2.5 mg/kg IM one injection, then ~1 month later two injections 24 h apart (Heartworm adulticide (3-injection AHS protocol)). Confirm against the label and the patient before use.

### Can Melarsomine be given to cats?

Not recommended in cats — adverse reactions (Not recommended).

### When should Melarsomine not be used?

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.

### What are the side effects of Melarsomine in animals?

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).

## Sources

- Plumb's Veterinary Drug Handbook
- AAHA guidelines
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.