Why do dogs need heartworm preventions?
Heartworms are one of the most successful parasites on the planet and dogs are incredibly susceptible to heartworm disease. It only takes the bite of one mosquito to infect a dog and only a few mosquito bites to create a fatal heartworm infection. Almost all dogs do their “business” outside and if they are not on heartworm prevention, this is enough time for the mosquitoes to bite and deliver their fatal package. Mosquitoes are common and unfortunately dogs have almost no internal defenses against infection. We know that one infected mosquito bite will deliver 3 to 8 infective larva from which between 2 and 5 heartworms will live to adulthood. We cannot prevent mosquito bites and we cannot kill all life stages of the heartworm with any single medication.
What is in heartworm prevention?
Heartworm preventatives all fall into the same group of “antibiotics” produced by different strains of the same class of Streptomyces species bacteria. This group of antibiotics is called macrocyclic lactones and include:
1) Ivermectin which is found in Heartgard, Iverhart Link to prevention
2) Milbemycin Oxime which is found in Interceptor, Sentinel, Trifexis Link to prevention
3) Selemectin which is found in Revolution Link to prevention
4) Moxidectin which is found in ProHeart 6, ProHeart12, Advantage Multi Link to prevention
When should heartworm prevention be given?
Because heartworms are transmitted by mosquitoes puppies can be infected at an early age. Preventions should be started as soon as it is safe for the puppy to start medications, usually between 2 and 3 months of age. The heartworm larvae injected into the dog by the mosquito take around 50 to 60 days to develop into adult heartworms. Heartworm preventions kill one or more of the larval stages; they can’t kill the adult heartworms. This means that preventions must be given often enough to ensure that no heartworm larvae are able to develop into adults. Oral and topical heartworm preventions are given as a once a month treatment. The heartworm prevention does not last 30 days but only a few days while it kills all the L3 and L4 heartworm larva in the pet.
Which heartworm prevention does Dr Garner recommend?
Ivermectin has been available for heartworm prevention for longer than any other preventions. Heartgard Plus is the most flavorful of the once a month oral medications for heartworm prevention. Heartgard Plus also has medication for the control of roundworms and hookworms. Because Ivermectin has been on the market longer there are now generic products available at a lower price. While these generic products may provide the same protection, in my opinion, none will have the excellent taste of Heartgard Plus. Generic Products include Tri-Heart Plus, IverHeart, Value Heart and others. Ivermectin containing products cannot be given to heartworm positive pets without risk for a severe reaction. See exceptions to this in the section on heartworm therapy.
Sentinel, Interceptor and Trifexis
Milbemycin Oxime is the active ingredient in Interceptor, Sentinel and Trifexis. These are oral medications that are administered as a “flavor tab” this tablet is slightly softer and has a better taste than most medications. Most pets will take it but in my opinion it is not as readily taken as Heartgard Plus. If it is refused by the pet, the pill can still be poked down the throat of the pet with minimal effort. Sentinel, Interceptor and Trifexis have the same medication for heartworm prevention. Sentinel has an additional medication that acts as a “birth control” for fleas. Trifexis has an additional product that kills adult fleas. As a part of a complete flea control program, Sentinel and Trifexis can be effective at controlling fleas, heartworms, hookworms and roundworms. Milbemycin Oxime must be only given to heartworm negative pets. Severe, sometimes fatal reactions have been reported when this medication is given to pets which have heartworms. This medication is safe at the dose for heartworm prevention, for collies and collie crosses and other pets which are sensitive to this class of drugs.
Selemectin is the active ingredient in Revolution. Revolution is applied to the skin surface once a month. It has minimal absorption into the body. It is very fat soluble and spreads across the hair coat using the oil on the hair and concentrates in the oil producing glands of the hair follicle. It is then released from the hair follicle over the period of a month. Enough selemectin is absorbed to kill heartworms particularly in small dogs and cats. But because in some studies it has been shown to be less effective in larger dogs I recommend other medications than Revolution for heartworm prevention. Revolution does control fleas, ear mites, ticks and sarcoptic mange.
Moxidectin is the active ingredient in ProHeart6 and ProHeart12. ProHeart is a formulation of slow release Moxidectin that prevents heartworms for 6 months (available in USA) or 12 months (available in Australia). This injectable product is associated with many side effects and veterinarians wishing to use it must first take a course and certify they are competent to use this product. ProHeart cannot be used in pets less than 6 months of age. I do not use or recommend ProHeart at this time but it may be useful in situations where monthly dosing or application is difficult.
Moxidectin is a remarkable substance that is both safe and effective as a heartworm prevention. Advantage Multi is a topical solution for application to the pet’s skin once a month.
- It is the only heartworm prevention that may be given to heartworm positive dogs.
- It is the only heartworm prevention that is effective against all strains of heartworms identified.
- It is the only heartworm preventative that kills early L5 or young adult heartworms.
Advantage Multi is a combined product of Moxidectin which prevents heartworms and controls intestinal worms (hookworms, roundworms and whipworms) combined with imidacloprid which kills adult fleas. I recommend Advantage Multi as the best Heartworm Prevention Available today. It has a broader range of effectiveness against the life stages of heartworms and is also effective against more species of intestinal parasites as well. It is safer than other products in the same category and can be given to puppies at 7 weeks of age and to heartworm positive animals. There is a new concern that heartworms are developing resistance to heartworm preventions. See this article that compares Advantage Multi to all the other common heartworm preventions.