Determination of terbinafine in tissues

Terbinafine and N-demethyl terbinafine concentrations were determined simultaneously in rat tissues by a high-performance liquid chromatography method. This method involved the homogenization of tissues (except for skin) followed by a liquid-liquid extraction. Skin samples were dissolved in sodium hydroxide prior to extraction. Terbinafine and its N-demethylated metabolite were assayed using a C(18) reversed-phase column with a mobile phase of acetonitrile and water (40:60) containing ortho phosphoric acid (0.02 M) and triethylamine (0.01 M), and UV detection (at 224 nm). The standard curve for the assay (constructed using clotrimazole as internal standard) was linear over the concentration range 100-3000 ng/g in skin and 10-600 ng/g in all other tissues. The inter- and intra-day precision for both terbinafine and metabolite was between 0.2% and 16%. The limit of quantification was 10 ng/g in all tissues and 100 ng/g in skin. This assay was found to be reliable and reproducible for the determination of terbinafine and N-demethyl terbinafine concentration in all rat tissues and has been used for tissue distribution studies.