Evaluation of persistence of terbinafine in the hair of normal cats after 14 days of daily therapy

This study determined the residual concentration of terbinafine in cat hair after 14 days of oral treatment. Ten clinically normal cats were administered terbinafine orally at a daily dose of 34–45.7 mg kg −1 for a total of 14 days. Areas of 15 cm 2 were shaved on the lateral thorax at day 0 and weekly for 8 weeks after the last dose of terbinafine. The hair samples were analysed by high‐pressure liquid chromatography to determine the persistence of terbinafine over time. The mean terbinafine concentration in hair was 2.30 ng mg −1 after 14 days of therapy. The half life was 1.84 weeks after the last dose of terbinafine. With a 99% confidence interval, the concentration of terbinafine remained in the cat hair at or above 0.03 ng mg −1 (minimal inhibitory concentration (MIC) 90  = 0.03 µg mL −1 ) for 5.3 weeks. Slight deviations in the complete blood cell count and serum chemistry values were not attributed to terbinafine. Four cats experienced vomiting during the terbinafine treatment; two of these cats also experienced intense facial pruritus followed by a macular to papular skin reaction 7–14 days after the discontinuation of terbinafine. In summary, terbinafine persists in hair at concentrations above the MIC for several weeks after stopping medication, even after short‐term therapy (14 days). These results suggest that pulse therapy of terbinafine should be further researched and potentially considered as a treatment modality for feline dermatophytosis, an approach that would decrease treatment duration while maintaining effectiveness.