Objective: To evaluate the efficacy of daily administration of ivermectin in the treatment of dogs with amitraz-resistant generalized demodicosis.
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.
Ivermectin: – For most dogs signs of toxicosis may be seen at doses greater than 2 mg/kg (0.9 mg/lb). Dogs affected by genetic sensitivity can have toxicosis with as little as 0.1 mg/kg (0.04 mg/lb). – Clinical signs of toxicosis in cats have been reported at doses of 0.3-0.4 mg/kg (0.1 mg/lb).
There are particular breeds of dogs that are sensitive to this drug class due to a genetic mutation (referred to as MDR1). Toxicosis may occur in these dogs even when therapeutic amounts are ingested. Dogs that are classified with this sensitivity include Australian Shepherds, Collies, English Shepherds, German Shepherds, Longhaired Whippets, McNabs, Old English Sheepdogs, Shetland Sheepdogs, and Silken Windhounds.
References: – Al-Azzam SI, Fleckstein L, Cheng K, et al. Comparison of the pharmacokinetics of moxidectin and ivermectin after oral administration to beagle dogs. Biopharm Drug Disposition 2007;28:431-438. – Mealey KL. Ivermectin: macrolide antiparasitic agents. In: Peterson ME, Talcott PA, ed. Small Animal Toxicology, 2nd ed. St. Louis: Elsevier, 2006. – Osweiler, G, et al. (2011). Blackwell’s five-minute veterinary consult clinical companion. Small Animal Toxicology. [Kindle version]. Retrieved from Amazon.com
Intoxication occurs in pets when small animals ingest medication intended for larger animals. It is very important to check the weight range and ensure your pet is receiving the correct dosage of medication. Dogs on farms or in rural environments are at a greater risk of toxicosis due to exposure of medication formulated for animals of greater weight/size. Toxicity may occur if your pet is exposed to the feces of large animals recently treated with these medications.