Complications From Canine Heartworm Medication

by Lydia Janssen
Preventative care is important, as heartworms can be fatal.

Preventative care is important, as heartworms can be fatal.

Chris Amaral/Digital Vision/Getty Images

A heartworm infestation is an extremely serious disease that can be fatal to your dog. While the monthly preventative treatment is mild and easily tolerated, the cure for heartworms will put a significant strain on your dog and in some cases, can be fatal itself. Talk to your vet about preventative measures and make an appointment immediately if you suspect your dog may have heartworms.

Heartworm Disease

Heartworm disease is a parasitic infestation of your dog's heart. The worms compromise the function of the heart, while their young, or microfilaria, can spread to the arteries, liver, lungs and other organs. There are no symptoms at the beginning of the infection, and the first sign that something may be wrong is a cough. In its moderate phase, the disease may cause difficulty exercising and abnormal lung sounds as well. In severe cases, your dog may suffer from difficulty breathing, loss of consciousness, enlarged heart and liver, unusual heart sounds, fluid in the abdomen and death. Early treatment is crucial to your dog's survival.

Eliminating Adult Worms

The first step of treatment is usually eliminating the adult worms. This is accomplished by administering a medication that will poison the worms. Caparsolate and immiticide are two of the most commonly used treatments, both of which contain arsenic. Caparsolate is delivered through IV or injection and may cause vomiting, diarrhea, kidney failure and death. Immiticide is both more effective at killing worms and has less serious side effects. Surgery may be necessary in severe cases, removing the worms through the jugular vein. Particularly sick or elderly dogs may need a period of rest and treatment with aspirin and a preventative heartworm drug before they can tolerate more in depth treatment.

First Treatment Aftercare

After treatment for the adult worms, it is crucial that your dog rest. He must not run, play, go for walks or engage in any exercise for at least a month. As the worms die, parts of them move through the circulatory system and are reabsorbed. Exercise during this time puts your dog at risk for pulmonary embolism or blockage of other arteries, which may be fatal. Watch you dog closely for especially red or pale gums, difficulty breathing, listlessness, fever, vomiting, bloody discharge or hindquarter paralysis during recovery, as these are signs of serious complications and may need immediate veterinary intervention.

Eliminating Microfilaria

After one month, your dog can generally tolerate treatment for the microfilaria, or young worms. You vet may recommend starting on a preventative heartworm medication to slowly eliminate the microfilaria, or an oral treatment to eliminate them more rapidly. The oral treatment Ivermectin, may cause serious side effects such as diarrhea, vomiting, lethargy, weakness or shock within the first 10 to 12 hours of treatment. Herding breeds such as collies, Shetland sheepdogs and Australian shepherds are particularly susceptible to shock and death from this treatment and usually given an alternative medication.

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