The combination of fipronil 10% plus (S)-methoprene 9% has been on the market in the United States since 2003, sold under the brand name Frontline Plus (merial.com). Although it is widely used and many experimental studies have demonstrated its efficacy, there is limited information about its effect in field conditions. A previous study examining efficacy in dogs naturally infected with Rhipicephalus sanguineus, the brown dog tick, showed that while the combination was extremely effective for killing adult ticks (98%), efficacy against immature stages was only 78%. The current study examined speed of kill, persistence of efficacy, and effect of water exposure on dogs naturally infected with the brown dog tick. Before treatment, all dogs were examined and numbers of adult and immature ticks were estimated. To measure speed of kill, animals were examined at 48 hours after treatment, and tick counts were again collected. After 48 hours, 96% of adults and 91% of immature ticks had been eliminated. Weekly examinations conducted to measure persistence of efficacy showed that the combination maintained efficacy above 93% through 4 weeks after treatment, for all tick stages. At 2 weeks after treatment, 6 dogs were soaked with plain water, and in the weeks that followed no significant differences were observed between these dogs and the nonbathed controls. This study demonstrates the high efficacy of the combination of fipronil 10% plus (S)-methoprene 9% against the brown dog tick and shows that efficacy is maintained even after a thorough soaking.

Commentary: In addition to ensuring the comfort of our beloved pets, tick bite prevention is an important public health measure. Keeping ticks off of pets helps control the transmission of tick-borne zoonotic pathogens, such as that causing Rocky Mountain spotted fever. Although it is not the predominant vector, the brown dog tick has recently been implicated in transmission of this pathogen in the southwestern states, where the incidence of the disease has been on the rise over the past decade, especially in Native American populations.

Efficacy of the fipronil 10% + (S)-methoprene 9% combination against Rhipicephalus sanguineus in naturally infested dogs: Speed of kill, persistent efficacy on immature and adult stages and effect of water. VET PARASITOL 170:96-103, 2010.