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 naturally 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 dosage of 6mgkg(-1) (range, 6-12. 5mgkg(-1)) or the vehicle only from the commercial formulation of selamectin (negative control). Treatments were administered 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 ears of dogs were examined otoscopically on day 14 for the presence of viable 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 ln(mite count+1) values were significantly (P< or =0.0015) lower for selamectin than for the vehicle for all animals on all count days. Thus, selamectin administered topically at a minimum dosage of 6mgkg(-1) was safe and 100% effective against naturally acquired aural infestations of O. cynotis in dogs and cats after a single dose or after two doses administered 1 month apart.