Efficacy of Ivermectin against Dirofilaria immitis larvae in dogs 31, 60, and 90 days after injection.

Ivermectin, given as a single oral dose of 0.05 mg/kg, prevented the maturation of Dirofilaria immitis in dogs if given at 31 or 60 days after infection. When treatment was delayed 90 days after injection, maturation of worms occurred in 3 of 5 dogs.