Efficacy of a topically applied spot-on formulation of a novel insecticide, metaflumizone, applied to cats against a flea strain (KS1) with documented reduced susceptibility to various insecticides

A spot-on metaflumizone formulation was evaluated in adult domestic short hair cats to determine its adultidical efficacy against a flea strain that has reduced susceptibility to a number of insecticides. Eight cats served as non-treated controls, eight cats were treated with a metaflumizone formulation at 0.2 ml/kg (40 mg metaflumizone/kg) and eight cats were treated with fipronil 10% w/v–(s)-methoprene 12% w/v at 0.075 ml/kg (7.5–7.7 mg fipronil/kg:9.0–9.2 mg (s)-methoprene/kg). On days −1, 7, 14, 21, 28, 35, and 42 each cat was infested with approximately 100 unfed KS1 cat fleas, Ctenocephalides felis. At approximately 48 h after treatment or infestation, each cat was combed to remove and count live fleas. Treatment with metaflumizone provided ≥99.3% efficacy for 3 weeks post-treatment and then 97.4, 91.4 and 86.2% efficacy at 4, 5 and 6 weeks post-treatment, respectively. Fipronil–(s)-methoprene provided 99.6% efficacy at 1 week post-treatment and then 97.6, 96.4, 71.3, 22.0 and 13.1% efficacy at weeks 2, 3, 4, 5 and 6, respectively. The reductions in flea numbers were significantly greater for the metaflumizone treatment than for fipronil–(s)-methoprene from 3 to 6 weeks after treatment.