Heartgard Plus and Tri-Heart Plus are monthly medications used to prevent heartworm infection and intestinal parasites in dogs. Heartworm is a serious and sometimes fatal condition for dogs that requires difficult treatment if contracted.
Heartworms, or Dirofilaria immitis, are transmitted to dogs and other animals through mosquitoes, which contract them from the blood of other infected hosts. The larvae, called microfilariae, are released by the adult female worm into the animal's bloodstream. In dogs, the larvae take roughly six months to grow into adult worms, which can reach up to 14 inches in length. The worms can live for five to seven years in the dog's heart and arteries of the lungs and can cause eventual heart failure and other organ damage. Symptoms in dogs are sometimes hard to detect in the early stages of infection, but include coughing, difficulty breathing, fatigue, a rough coat and weight loss.
Both Heartgard Plus and Tri-Heart Plus are used in dogs to prevent heartworm, hookworm and roundworm infection. The active ingredients are the same: ivermectin and pyrantel. The medications work by eliminating the heartworm larvae in your dog before they mature.
These two medications are similar and both come in packs of six flavored chewables with different color-coded dosages by dog weight. Both Heartgard Plus and Tri-Heart Plus have been proven safe for dogs six weeks and older and can be used for small dogs and dogs that are pregnant or breeding. Tri-Heart Plus claims to offer all of the same benefits as Heartgard Plus, but at a lower price.
Both Heartgard Plus and Tri-Heart Plus should be given to your dog orally once a month, preferably near the same day. To be effective, the first dosage of either one has to be given to your dog within one month of its first exposure to mosquitoes. If you are replacing one with the other, or switching from a different medication, make sure not to wait more than a month between doses. If the time between doses exceeds one month, the ivermectin might not be as effective. As with any medication, don't use either one after the expiration date.
Remember, both of these medications are used to prevent heartworm infection, not to treat it. The ivermectin is effective in preventing the growth of larvae but cannot be used to clear existing microfilariae or adult worms. Your dog should be tested for an existing infection before starting treatment, again after six months, and annually. If your dog is infected, it must be treated to remove the heartworms and larvae before you start a preventative medication routine. Some similar adverse reactions in dogs have been reported in clinical trials for both Heartgard Plus and Tri-Heart Plus. These include depression, lethargy, vomiting, anorexia, diarrhea, pupil dilation, decreased muscle coordination, convulsions and hypersalivation. Trials also show that some Collies are more sensitive to ivermectin at elevated levels than other breeds.