Heartgard Plus Side Effects

Heartworm disease is a potentially deadly infection that dogs acquire through mosquito bites. Veterinarians often prescribe heartworm preventatives to protect dogs from this disease. Heartgard Plus is one of the most commonly prescribed such medications. Like any medicine, however, it can cause side effects.

Heartworms

According to Doctors Foster and Smith, a pet-supply and informational website, mosquitoes contract immature versions of heartworms when they bite an infected animal. Once inside a mosquito's body, heartworms develop into larvae. When the infected mosquito bites other animals, it passes the larvae on to them.
When a dog contracts heartworms, the larvae migrate to the dog's heart, where they grow into mature worms that may measure up to 14 inches in length. The worms clog the heart and blood vessels leading to and from it, and eventually they can migrate to other organs as well. Untreated heartworm disease can kill a dog.

Prevention

To prevent dogs from developing heartworm disease, veterinarians prescribe heartworm preventatives, which are usually administered once a month in the form of chewable meat-flavored tablets. Before a dog starts on a regime of a heartworm preventative, the vet will run a blood test to make the animal isn't already infected.

Heartgard Plus Side Effects

Merial, an international company that manufactures Heartgard Plus as well as other products for animal health, lists adverse reactions to the medication on its website. Side effects that may occur with 24 hours of dosing include vomiting and diarrhea in 1.1 percent of animals tested. Other, longer-lasting side effects include lethargy, depression, anorexia, prolonged and abnormal dilation of the pupils (mydriasis), involuntary muscle movements (ataxia), staggering, convulsions and excessive salivation.

Collies and Heart Gard Plus

The active ingredient in Heartgard Plus is ivermectin. Some collie breeds of dogs are sensitive to ivermectin, which at elevated dosages can cause mydriasis, depression, ataxia, tremors, drooling, paresis (impaired movement), recumbency, excitability, stupor, coma and death.
Merial contends that the dosage of ivermectin required to cause these reactions in collies is more than 16 times the target dosage in dogs. It has tested Heartgard Plus on collies at levels more than 10 times the recommended dose, and reports no adverse side effects. Thus Merial concludes that Heartgard is safe for collies when taken at the recommended dose.

Solution

If you think your dog is having a bad reaction to Heartgard Plus, call your vet or your local emergency animal hospital immediately and speak with one of the doctors there. These professionals can assess how severe the reactions are and advise you about what actions you should take to help your pet recover.

References

• Doctors Foster and Smith: Heartworm FAQ
• Heartgard Plus Chewables