Veterinarians who use high, extralabel doses of ivermectin to treat dogs with nonresponsive demodectic mange and other conditions should be aware that the Food and Drug Administration's Center for Veterinary Medicine has received reports of some dogs developing signs of ivermectin toxicosis when ivermectin is used concurrently with Comfortis (spinosad).
The clinical signs of these adverse reactions are consistent with ivermectin toxicosis.
Elanco Animal Health, a division of Eli Lilly and Company, manufactures Comfortis. The drug is a monthly oral, chewable tablet for the prevention and treatment of flea infestations on dogs.
The FDA and Elanco Animal Health are advising veterinarians that dogs receiving extralabel doses of ivermectin should not receive concurrent treatment with Comfortis.
Eli Lilly has issued a Companion Animal Health Technical Bulletin on "Spinosad and the Extra-Label Use of High Dose Ivermectin for the Treatment of Generalized Demodicosis in Dogs" at http://elms.xh1.lilly.com/10788_03_tech_Bulletin.pdf (PDF, 1.5 MB).