Levamisole resinate as a Dirofilaria immitis microfilaricide in dogs

Dogs infected naturally or experimentally with Dirofilaria immitis were given levamisole resinate at the rate of 5.5 or 11 mg/kg of body weight/day for 10 days. All dogs had been treated with thiacetarsamide sodium approximately 6 weeks earlier. When given at the dosage of 5.5 mg/kg for 10 days, levamisole resinate was not effective as a microfilaricide in either naturally or experimentally infected dogs. Microfilaria counts were reduced in all dogs at this dosage, but never to zero. In all cases where the higher dosage (11 mg/kg) was used, microfilaria counts were reduced to zero within 10 days. Signs of toxicosis were noticed in only 2 experimentally infected dogs, both of which were found to be harboring live adult male D immitis at necropsy.