Ivermectin for treatment of generalized demodicosis in dogs

Objective: To evaluate the efficacy of daily administration of ivermectin in the treatment of dogs with amitraz-resistant generalized demodicosis.

Design: Prospective, clinical trial.

Animals: Twelve privately owned dogs with juvenile-onset or adult-onset generalized demodicosis that had failed to respond to biweekly or weekly applications of 0.025% amitraz solution.

Procedure: All dogs were treated with undiluted ivermectin at a dosage of 0.6 mg/kg of body weight, PO, every 24 hours. There was no other parasiticidal agent given topically or systemically. A physical examination and multiple skin scrapings were performed every 2 to 4 weeks while dogs were receiving ivermectin. Skin scrapings were performed at approximately the same sites at every examination. After no mites were seen, treatment was continued for at least 2 more weeks and then stopped. Dogs were reexamined, and skin scrapings were repeated if any skin lesions developed. For dogs that remained clinically normal, follow-up information was obtained by telephone. Dogs that were free of clinical signs of demodicosis 12 months after ivermectin administration was discontinued were considered cured.

Results: Ten of 12 dogs were cured. Median duration of treatment for these dogs was 10 weeks (range, 6 weeks to 5 months). Two dogs were failures, relapsing 10 months and 11.5 months after treatment was stopped. One of these dogs was successfully treated with a second course of ivermectin. Mild ivermectin toxicosis developed in 1 dog after 6 weeks of treatment; side effects resolved shortly after the treatment was stopped.

Clinical implications: Daily use of ivermectin, at a dosage of 0.6 mg/kg, PO, was found to be effective in the treatment of generalized demodicosis in dogs.