Determination of terbinafine in nail samples during systemic treatment for onychomycoses

A combination of alkali treatment and proteinase K digestion was used to solubilize nail samples from patients with onychomycosis treated orally with terbinafine. The samples were extracted and the levels of terbinafine and its metabolite measured by high-pressure liquid chromatography. The results showed a relatively rapid penetration of terbinafine into normal nail plate, suggesting that diffusion via the nail plate is the primary route of entry into this tissue. The levels of terbinafine achieved in nail samples exceeded the range of MICs for dermatophytes at the earliest time point (4 weeks) tested in 50% of patients and remained stable, without accumulation, during periods of treatment of up to 3 months.