Diarrhea Reaction To Heartworm Medication. Dogs are routinely hospitalized for heartworm treatment, so they can be treated for the side effects as well. Prevents heartworm larvae from reaching the dog's heart.
In the case of an allergic response to the heartworm medication, a dog may experience itching, hives, swelling of the face, or even seizures or shock. A dog who reacts to something like heartworm medicine is at risk for being in pain, getting hives or itching, swelling of the face or even receiving shock or seizures. Hair loss at the application site has also been reported.