Heartworm Treatment: Navigating a Changing Landscape

Abstract

Treatment of canine heartworm (Dirofilaria immitis) has always been a difficult endeavor, whether it is due to a perceived complicated treatment regimen, the potential for post-treatment complications, or the practical consideration of cost by the owner. Currently, there exists only one FDA-approved drug that is labeled for treatment of adult heartworms, which is melarsomine dihydrochloride (ImmiticideTM). Some practitioners and clients are questioning the use of melarsomine for removal of adult heartworm due the reasons mentioned above. While the numbers of practitioners and clients who maintain this opinion have not been documented, some are quite vocal in numerous social media outlets. This has led to an interest in the colloquially named “slow-kill” or “soft-kill” method, which is more accurately defined as the continued use of an ivermectin-based heartworm preventive medication in a heartwormpositive animal. What makes the situation even more confusing is that heartworm research is very difficult to perform due to the relatively lengthy life cycle of the parasites and the lack of rodent experimental models. This has led to many of our current recommendations being based on opinion, or people’s “best guess,” rather than evidenced-based experiments. There is no agenda connected with these recommendations; rather, the data has not been gathered to completely support the recommendations. While this article is supposed to discuss the current data regarding heartworm treatment, the fact is that there is a relative lack of data pertaining to the treatment and pathophysiology of canine heartworm disease. Many of the points discussed in this article are based on my interpretation of what data does exist in combination with the current recommendations of the American Heartworm Society (AHS).1