The efficacy of selamectin in the treatment of naturally acquired aural infestations of Otodectes cynotis on dogs and cats

The efficacy of a novel avermectin, selamectin, was evaluated against natur ally acquired aural infestations of Otodectes cynotis on dogs and cats. In four controlled and masked studies conducted in the USA and Europe, animals were allocated randomly to treatment with either selamectin at a minimum d osage of 6 mg kg(-1) (range, 6-12.5 mg kg(-1)) or the vehicle only from the commercial formulation of selamectin (negative control). Treatments were a dministered topically in a single spot to the skin of each animal's back at the base of the neck in front of the scapulae. Cats were treated on day 0 only, and dogs were treated either on day 0 only or on days 0 and 30. The e ars of dogs were examined otoscopically on day 14 for the presence of viabl e mites, Mite counts were conducted on day 30 for animals that had received one dose and on day 60 for animals that had received two doses. Percentage reductions in geometric mean mite counts for selamectin treatment compared with the vehicle were 100% for all animals on all count days. Analysis of variance, confirmed by Savage Scores, showed that In(mite count+1) values w ere significantly (P less than or equal to 0.0015) lower for selamectin tha n for the vehicle for all animals on all count days. Thus, selamectin admin istered topically at a minimum dosage of 6 mg kg(-1) was safe and 100% effe ctive against naturally acquired aural infestations of O. cynotis in dogs a nd cats after a single dose or after two doses administered 1 month apart. (C) 2000 Elsevier Science B.V. All rights reserved.