Efficacy of selamectin in the treatment and prevention of flea (Ctenocephalides felis felis) infestations on dogs and cats housed in simulated home environments

The efficacy of selamectin, a novel avermectin, in protecting dogs and cats against experimentally induced environmental flea (Ctenocephalides felis f elis) infestations, was evaluated in a series of controlled and masked stud ies. Purpose-bred shorthaired cats and Beagles were randomly allocated to t reatment with either selamectin at a minimum dosage of 6 mg kg(-1) of body weight in the commercial formulation or the negative control treatment (veh icle only), and housed in controlled simulated home environments capable of supporting the flea life cycle. Day 0 was defined as the first day of trea tment. Treatments were administered topically in a single spot on the skin at the base of the neck in front of the scapulae. In environmental challeng e studies, which were designed to evaluate the efficacy of selamectin in th e treatment and control of established flea infestations, dogs and cats wer e each infested with 100 fleas on days -28 and -21 and placed in carpeted r ooms in order to establish high levels of active flea infestation prior to day 0. Treatments were administered monthly for 3 months. Flea comb counts were performed on days 14, 29, 44, 59, 74, and 90. Reductions in geometric mean flea comb counts for selamectin, compared with vehicle, were >99% from day 14 onwards for dogs, and >92% on day 29 and >99% on days 44, 59, 74, a nd 90 for cats (P=0.0001). In prevention of environmental infestation studi es, dogs and cats were placed in environments capable of supporting flea in festations and given monthly treatments for 2 months, commencing on day 0, Animals were infested with 100 fleas on days 1 and 7, and flea comb counts were performed on days 29, 44, and 60. Reductions in geometric mean flea co mb counts for selamectin, compared with vehicle, were >99% on days 29, 44, and 60 (P=0.0001) for dogs and cats. Monthly administration of selamectin t o dogs and cats housed in environments highly suited to completion of the f lea life cycle was shown to be highly effective in the treatment and preven tion of flea infestations, without the need far supplementary environmental control measures. (C) 2000 Elsevier Science B.V. All rights reserved.