Efficacy of ivermectin in hookworms as examined in Ancylostoma caninum infections

Single oral doses of ivermectin were given to dogs with moderate or heavy infections of Ancylostoma caninum (egg counts ranging from 7,100 to 41,700 eggs/g feces) at 100, 50, 30, or 10 micrograms/kg body weight. Each of these dosages was effective in clearing the infection completely, so that numerous worms were passed in the feces on days 1-3, but no worm was recovered from the intestinal tract at necropsy on day 4 after treatment. In contrast, an average of 178 worms per dog was recovered at necropsy from the vehicle-treated control and the untreated animals. Albendazole, a known anti-hookworm agent, even in a dose of 400 mg, eliminated only 21-65% of the worms harbored by the infected animals. No untoward reaction to ivermectin or significant pathological change was noted in the experimental animals. In vitro experiments demonstrated that ivermectin: (1) was highly detrimental to actively motile adult worms in concentrations greater than 5.60 micrograms/ml; (2) was detrimental to eggs inside the uterine tissue of female worms in dosages at or greater than 10 micrograms/kg body weight; and (3) killed infected larvae in concentrations as low as 0.0025 micrograms/ml.