Preventatives, Part 2:

April 2021

This month, I will continue the discussion about common parasites and the preventatives we prefer to use to treat and prevent them. I’ll talk about heartworms, since they are the most potentially harmful of these parasites.

Heartworms in a dog are very common throughout the American south due to the climate. They are spread from dog to dog via mosquitoes, which feed on blood from one dog, pick up the heartworm larvae in the blood and then spread the parasite when it feeds on another dog. The heartworm life cycle with multiple larvae life cycles prior to adult heartworm develop is complex, and the overall process from 1st stage of larvae to adult heartworm is about 7 months in duration. This means puppies under 7 months cannot have heartworm disease, but we want to start the preventatives as soon as possible when they are young. The bottom line is that we want to prevent dogs from developing heartworm disease, which involves the adult heartworms living in the lungs, and in the worst-case scenario, in the heart. When dogs have the full-blown heartworm disease, it is potentially fatal because it can lead to heart failure in its end-stage. Also, if a dog has heartworm disease for a significant time in its life but is treated successfully (meaning adult heartworms are eradicated from the body), it can still have long-lasting effects to its lungs and heart that need to be managed. This is why we recommend heartworm preventatives for every one of our canine patients, and that is given all 12 months in the year.

Heartworm preventatives come in several forms. The most typical type is the chewable tablet that is given monthly. When it is given monthly, the medication kills heartworm larvae in the blood. This prevents adult heartworms from developing in the body, thus preventing potential disease. There are topical forms as well, which are placed on the skin monthly, performing the same functions as the chewable tablet. The tablet and topical preventatives are prescription medications, meaning we need to have a doctor-patient-owner relationship in order to dispense this medication. The last form is an injectable medication specially formulated for slow release under the skin that can last 6 or 12 months in the body to prevent the development of the adult worms. The last form makes it very convenient for the owner because they do not have to remember to give the preventative at home, and it is guaranteed that the dog will have the preventative in its body for six months or a year.

At St. Francis Hospital for Animals, we recommend the type of preventative that is the best fit for our patients. Prior to six months of age, we prefer the monthly tablet because they are growing quickly, and thus outgrow certain doses of medication within weeks or a month. After they reach six months, the injectable medication called Proheart is usually the best preventative for our doggy patients. Like I mentioned before, the owner doesn’t have to remember to give the medication AT ALL, and it is guaranteed that are getting the preventative for that time period. Rarely, a dog may have an anaphylactic reaction to this injection, which we would treat immediately at the hospital. This is very uncommon, if it happens to one of our patients, we would not use Proheart with that patient again. In dogs that do not receive Proheart injections, we have several

options, Heartgard, Sentinel Spectrum, and Trifexis, all chewable tablets that are given monthly. Taste of the tablets can be a problem with some dogs however, and they will not eat them, the owner may either hide it in a treat, or place it in the back of the throat of the animal. Most owners prefer not to jam anything down their dog’s mouth! So, another reason we prefer to give the injectable form for some patients is that palatability is not an issue, freeing owners from having that hassle of their dog refusing the preventative at home.

Lastly, I will discuss the concept of owner compliance of giving the preventatives at home. Like I mentioned before, we recommend that the preventatives are given all year long for the most effective prevention of heartworm disease. A problem is that a majority of owners don’t follow that schedule, and often forget to give the medication consistently. In a published study, the percentage of owner compliance when giving heartworm preventative all year-long was about 15% in clinics throughout the country. We know that it can be hard to remember every month to give the medication to your, life happens! Again, we prefer the Proheart injectable preventative because you DON’T HAVE TO REMEMBER anything! It will be guaranteed that your dog will be heartworm free, for 6 to 12 months.

In conclusion, heartworm preventatives are one of the most important medications that we recommend for our canine patients. They come in several formulations, and we choose the one that is best suited to our individual patients. If you have any questions, please let us know, give us a call or ask at your next visit. Next month, I will wrap up the discussion on parasites with an article on intestinal parasites. Gross!! Have a great spring!

Dr. Jaime Kozelka
St. Francis Hospital for Animals