Melarsomine is an organic arsenical chemotherapeutic agent that is used in a veterinary hospital setting to treat dogs that are suffering from heartworm disease.

Melarsomine for Treating Canine Heartworm

How Melarsomine Works

Melarsomine contains arsenic, which is the active ingredient that kills both the adult heartworm and immature (>4 months old) heartworm. In some cases, doxycycline and/or prednisone are also administered to the patient to help manage the side effects commonly produced by the arsenic. After treatment with melarsomine, the patient should undergo cage rest for four to six weeks.

Potential Side Effects of Melarsomine

The most common side effects of melarsomine include pain, swelling, and tenderness at the injection site; fever, lethargy, a loss of appetite, vomiting, gagging, lung congestion, and depression. Hard nodules may also develop and persist at the injection site. Older dogs, such as those aged eight years or older, tend to be more susceptible to depression, vomiting, and loss of appetite as compared to younger patients.

More severe side effects of melarsomine, although rare, include abnormal heart rhythms, coughing up blood, diarrhea, excessive drooling and panting, and death.

It is important to note that there are risks to using melarsomine, because it kills a large number of heartworm very rapidly; this can sometimes cause problems for the patient. In cases of severe infestation (Class 4 heartworm disease), treatment can even prove fatal.

For this reason, surgical removal of the heartworm is recommended to help improve the patient’s prognosis. Remember, if left untreated, then heartworm disease will prove fatal, so the risks of treatment are usually accepted.

Precautions & Drug Interactions With Melarsomine

Although melarsomine is FDA-approved for use in canines, there are certain situations where the drug should be avoided or used with extreme caution. For instance, if the pet has a known allergy to melarsomine, then it should be avoided. This medication should also be used with extreme caution in patients that are pregnant, nursing, or already receiving treatments for other diseases, especially those affecting the kidneys or lungs.

Melarsomine is only approved for use in dogs. It should never be administered to cats or to other pets.

Melarsomine has been shown to interact with Caparsolate and glucocorticoids, so extra care needs to be practiced in these types of cases.

Dosage and Administration of Melarsomine

Melarsomine comes formulated in powder form that is reconstituted and administered via intramuscular injection deep in the muscle of the patient’s lumbar, or lower back, area.

In cases where the dog has Class 1 or 2 heartworm disease, a second dose is usually administered 24 hours after the first dose, with a second round of treatment four months later if the tests show the continued existence of heartworm in the patient.

Dogs with Class 3 or 4 heartworm disease will usually receive a more aggressive treatment based on the veterinarian’s directions. Depending on the severity of the infection, surgical removal of the heartworm from the vena cava may be required.

How to Store Melarsomine

When it is in its powder form, melarsomine should be stored upright at room temperature. Once reconstituted, however, the medicine should be stored in the refrigerator. Melarsomine should be disposed of if not used within 24 hours after reconstitution.

Author: Giano Panzarella