Paul Pion, DVM, Dipl. ACVIM

The query from Dr. Warren Kaplan regarding the safety of heartworm prophylaxis medications in heartworm-positive dogs deserves to be addressed. On the American Heartworm Society Web site (www.heartwormsociety.org/AHS%-20Guidelines-Canine.htm) it is clearly stated that: "The macrocyclic lactones may be administered to heartworm-infected dogs with few or no microfilariae. However, dogs with moderate to high microfilarial levels should be carefully monitored following administration of these drugs, as they are the most effective microfilaricides available."