In 2008, researchers discovered that combination ivermectin and doxycycline treatment had strong adulticidal effects on heartworms in experimentally infected dogs.1 The current study sought to confirm that result in naturally infected animals, with a modified and more feasible dosage schedule. Eleven infected dogs were administered doxycycline, 10 mg/kg Q 24 H, for 30 days, along with ivermectin-pyrantel, 6 mcg/kg to 14 mg/kg, every 15 days for 180 days. All dogs were microfilaria-negative by day 90, and 8 of 11 were antigen-negative by day 300. Six of the 7 dogs that had visible parasites at the onset were negative by echocardiography by day 300. The gradual death of adult worms with use of this method eliminates the pulmonary thrombosis that can occur with other adulticide therapies.

1. Combined ivermectin and doxycycline treatment has microfilaricidal and adulticidal activity against Dirofilaria immitis in experimentally infected dogs. Bazzocchi C, Mortarino M, Grandi G, et al. INT J PARASITOL 38:1401-1410, 1998.

2. A combination of doxycycline and ivermectin is adulticidal in dogs with naturally acquired heartworm disease (Dirofilaria immitis). Grandi G, Quintavalla C, Mavropoulou A, et al. VET PARASITOL 169:347-351, 2010.