Initial evaluations of the effectiveness of spinetoram as a long-acting, oral systemic pulicide for controlling cat flea (Ctenocephalides felis) infestations on dogs

Spinetoram is a semi-synthetic, spinosyn class natural product derived from fermentation by the actinomycete, Saccharopolyspora spinosa. Based on LD50 (50% lethal dose) values against adult cat fleas (Ctenocephalides felis) using an in vitro contact assay, spinetoram was approximately 4-fold more potent than spinosad. Subsequently, two parallel-arm, randomized block design laboratory studies were conducted to evaluate the effectiveness of orally administered spinetoram against experimental C. felis infestations on dogs, when administered as a single dose or multiple doses over a 6-12 h interval. In the first study, 16 mixed-breed dogs were allocated to two treatment groups of eight dogs each, based on pre-treatment flea retention rates: negative (placebo) control; and a single dose of spinetoram at 30 mg/kg. In the second study, 32 mixed- and pure-breed dogs were allocated to four treatments groups of eight dogs each, based on pre-treatment flea retention rates: negative (placebo) control; a single dose of 60 mg/kg; three sequential 20 mg/kg oral doses evenly administered over a 6 h period; and three sequential 20 mg/kg oral doses evenly administered over a 12 h period. In both studies, treatments were administered to dogs in a fed state in order to enhance absorption of spinetoram. Therapeutic efficacy was assessed 24 h after treatment and persistent efficacy was assessed 48 h after each subsequent flea infestation. The duration of effectiveness was assessed at approximate weekly intervals beginning on Day 5 through Day 56 in the first study, or through Day 105 in the second study. In both studies, treatment efficacy was ≥99% (geometric means) through 44 d, with ≥99% efficacy continuing through 72 d for all three treatments in the second study. Efficacy remained ≥90% for at least 8 weeks with a single 30 mg/kg dose; through 13 weeks with three sequential 20 mg/kg doses; and through 15 weeks with a single 60 mg/kg dose. For all time points and in both studies, spinetoram-treated groups had significantly fewer live fleas relative to their respective negative control group (p < 0.05). The pharmacokinetic profile in dogs revealed that the mean plasma concentration of spinetoram required for effectiveness against fleas was maintained for at least 3 months regardless of whether the 60 mg/kg total body dose was administered as a single bolus or in three sequential 20 mg/kg doses administered over a 6-12 h period of time. The results of preliminary in vitro and in vivo studies demonstrate that orally administered spinetoram was well tolerated, and provides long lasting effectiveness against C. felis infestations on dogs.