Safety of moxidectin in avermectin-sensitive collies

Objective-To evaluate the safety of moxidectin administration at doses of 3 0, 60, and 90 mu g/kg of body weight (10, 20, and 30 times the manufacturer 's recommended dose) in avermectin-sensitive Collies. Animals-24 Colies. Procedure-Collies with mild to severe reactions to ivermectin challenge (12 0 mg/kg; 20 times the recommended dose for heartworm prevention) were used. Six replicates of 4 dogs each were formed on the basis of body weight and severity of reaction to ivermectin test dose. Within replicates, each dog w as randomly allocated to treatment with oral administration of 30, 60, or 9 0 mu g of moxidectin/kg or was given a comparable volume of placebo tablet formulation. Dogs were observed hourly for the first 8 hours and twice dail y thereafter for 1 month for signs of toxicosis. Results-Signs of toxicosis were not observed in any control group dog throu ghout the treatment observation period. Likewise, signs of toxicosis were n ot observed in any dog receiving moxidectin at 30, 60, or 90 mu g/kg. Conclusions and Clinical Relevance-The moxidectin formulation used in the s tudy reported here appears to have a wider margin of safety than ivermectin or milbemycin in avermectin-sensitive Collies.