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Melarsomine (Immiticide)
Veterinary & Aquatic Services Department, Drs. Foster & Smith
Heartworm
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Summary

Melarsomine is an injectable drug for in-hospital use to kill adult heartworms in dogs. Treatment (not prevention) of heartworm infection can result in fatal complications, but death from the untreated heartworm infection is far more likely. Dogs must have 4-6 weeks of cage rest following treatment.

Generic Name
Melarsomine

Brand Name
Immiticide

Type of Drug
Antiheartworm

Form and Storage
Available as a powder which is reconstituted (mixed with sterile water) before use.
Store powder upright at room temperature. Once reconstituted, store in refrigerator protected from light and use within 24 hours.

Indications for Use
An arsenic-containing compound used to kill immature (4+ month old) and adult heartworms (Dirofilaria immitis) in dogs.

General Information
FDA approved for use in dogs. Used in a hospital setting. Heartworm disease can kill, but it is preventable using the daily or monthly heartworm prevention medications. Routine heartworm testing is recommended even for those dogs on heartworm prevention year-round because the earlier heartworm disease is detected, the better the chance of a full recovery. Heartworm disease is graded Class 1-4 with 4 being the most serious. A heartworm preventive can be given at the same time as treatment with Immiticide.

Melarsomine is preferred over another drug, thiacetarsamide, that kills adult heartworms because it is less likely to cause a reaction where injected, it is more effective, less likely to cause liver damage, and can be used more safely in dogs with severe heartworm disease.

Usual Dose and Administration
Given intramuscularly (IM) deep in the lumbar (back) muscle. Do not administer at any other site. Alternate sides. Usually given twice 24 hours apart for animals with Class 1 or 2 heartworm disease. May need second round of treatment 4 months later depending on repeated test results. Dogs with other classes of heartworm disease may receive different doses/timing to decrease risk of complications. Given in a hospital setting to allow for the necessary supervision of the patient.

Side Effects
May see pain, swelling, and tenderness at the injection site or reluctance to move due to pain at injection site. Firm nodules can persist indefinitely. May also see coughing, gagging, depression, lethargy, lack of appetite, fever, lung congestion, and vomiting. Less commonly seen are excessive drooling, panting, diarrhea, coughing up blood, abnormal heart rhythms, and death.

Contraindications/Warnings
Not for use in dogs with Class 4 disease until the heartworms are removed surgically from the vena cava (large vein carrying blood back to the heart), as the risk of death is increased.

Animals with other diseases should be treated only with intense monitoring.

Death of the worms may cause coughing, fever, or weakness.

The dog must be kept quiet (cage rest) for 4-6 weeks after treatment to help decrease the risk of pulmonary embolism.

Repeat the antigen heartworm test 4 months after treatment.

Treating the heartworm disease may kill the pet, but if not treated, the heartworm disease is likely to kill the pet.

Use with caution in pregnant or nursing animals if unable to wait until a later date to treat.

Drug or Food Interactions
None known, although with another drug (Caparsolate) used to kill adult heartworms, glucocorticoids have a protective effect on adult heartworms, i.e., Caparsolate is less effective if the dog is also receiving glucocorticoids.

Overdose/Toxicity
Low margin of safety. Need to have an accurate weight before treating. May see damage to the lungs or kidneys. May see drooling, panting, restlessness, fever, vomiting, diarrhea, tremors, lethargy, staggering, and difficulty breathing which may progress to collapse, coma, and death. A possible antidote for an overdose is BAL in Oil Ampules (Dimercaprol Injection, USP). It is listed in reports as an antidote for arsenic toxicity.


Keep this and all other medications out of the reach of children and pets.


If you think your pet has been poisoned...

Contact your veterinarian or one of the Animal Poison Hotlines (listed below) if you think your pet may have accidentally received or been given an overdose of the medication.

**ASPCA National Animal Poison Control Center

1-888-4ANI-HELP (1-888-426-4435). $65.00 per case, billed to caller's credit card.

Follow-up calls can be made for no additional charge by dialing 888-299-2973.

There is no charge when the call involves a product covered by the Animal Product Safety Service.

**Pet Poison Helpline - 24-hour service available throughout North America for pet owners and veterinary professionals who require assistance with treating a potentially poisoned pet.

1-800-213-6680 ($35.00 per incident). Staffed 24-hours a day.


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