Drug efficacy of terbinafine hydrochloride (Lamisil) during oral treatment of cats, experimentally infected with Microsporum canis.

Cats represent a primary source of Microsporum canis infections in humans. Terbinafine hydrochloride (Lamisil) is commonly used in the treatment of microsporosis in humans as its fungicidal action permits short periods of treatment. The aim of the present study was to estimate the efficacy of the drug in cats. Nine cats were experimentally infected with M. canis and treated with terbinafine hydrochloride at a dose of 10-20 mg/kg (once daily, SID; low-dose group, LDG). Another nine cats were similarly infected and treated with 30-40 mg/kg SID (high-dose group, HDG) and a further nine cats were also infected and left untreated (control group, CG). The general condition of the cats was observed daily and their clinical symptoms evaluated weekly. The cats recovery was monitored using the Wood's lamp illumination test and microscopic and fungal culture examinations. The general condition of the cats during the study was good. The cure rates of the LDG were not significantly different from the CG at any period during the treatment. However, the HDG cure rates differed significantly from the other two groups. After 109 days of treatment, when all nine cats of the HDG were healed, seven cats of the LDG and all the cats in the CG were still M. canis-positive. This study shows that dosages of 10-20 mg/kg SID of terbinafine hydrochloride are not sufficient to terminate an experimental M. canis infection in cats within an acceptable period of time. Terbinafine hydrochloride can be used to treat dermatophytosis in cats, but a higher dosage, 30-40 mg/kg SID, should be used to achieve a cure.