Information on Heartgard for Dogs

Heartgard-brand medicines are used to treat and prevent dog heartworm infestations, as well as roundworms, hookworms and gastrointestinal parasites. Heartworms are parasitic worms that are transmitted by mosquitoes and live in an animal's heart and blood vessels. Heartworm infestation is a serious, possibly fatal condition that must be treated but is best prevented.

  1. Heartgard Products

    • Heartgard products are made by Merial and include Heartgard, Heartgard Plus and Heartgard Immiticide. Heartgard Plus treats roundworms, hookworms, heartworms and gastrointestinal parasites, in addition to heartworms. By eliminating heartworms in the tissue stage of the larvae, this medicine is a preventative treatment usually administered monthly. Immiticide is used to kill existing adult heartworm populations in a dog that has already been infected.

    Administering Heartgard Products

    • Heartgard Plus is administered once monthly as a beef-flavored chewable. According to Vetinfo, the entire dosage must be chewed (not swallowed whole) for it to be effective. This prescription treatment is available in three strengths, depending on the dog's weight.

      Heartgard Immiticide must be injected into the dog's lower back area once a month. These injections may produce soreness, nose bleeds, cough and fever, according to Vetinfo--some of which can be treated with medications.

    Active Ingredient in Heartgard Products

    • The active ingredient in Heartgard and Heartgard Plus is ivermectin, which is also used to kill ear mites, sarcoptic mange and demodectic mange. Though the latter two have not been approved as a use of this medication by the Food and Drug Administration, Vetinfo reports vets have found ivermectin-based drugs to be effective for these manges.

    Genetic Sensitivies to Heartgard Ingredients

    • Some breeds are genetically prone to be sensitive to Heartgard's ivermectin. The breeds most prone to this are collies, Shetland sheepdogs and Old English sheepdogs. Not every individual within those breeds will exhibit this sensitivity, and some dogs in other breeds have the sensitivity. A blood test can determine if it is present. Even with sensitivities, Heartgard can still be used--depending on the recommendation of your vet--but the dog will need additional monitoring.

    Side Effects of Heartgard

    • According to Vetinfo, possible side effects of Heartgard include depression, lethargy, diarrhea, vomiting, lack of appetite, seizures, lack of coordination, excessive salivation and dilated pupils. Vetinfo warns that if your dog has dilated pupils or lack of coordination after taking Heartgard, take him immediately to your clinic or animal hospital. Vetinfo also instructs owners to inform their vets of any medications the dogs are taking--even over-the-counter flea medications--before administering Heartgard products, as there can be interactions.