Detection and relevance of naftifine hydrochloride in the stratum corneum up to four weeks following the last application of naftifine cream and gel, 2%.

Background: Two-week treatment using naftifine cream or gel, 2% has been shown to be efficacious in subjects with Tinea pedis and/or Tinea cruris, and in most cases, continued improvement has been observed following cessation of treatment for up to four weeks. One possible explanation for continuous post-treatment improvement is drug-levels remaining in the stratum corneum (SC) as a function of time.

Objective: The objective is to use tape stripping methodology to assess the amount of drug available in the SC over a 28 day period following the last dose.

Methods: This was an open-label, single-exposure study on subjects comparing the amount of drug that was absorbed into the SC following topical application for 2-weeks. Twelve subjects were dosed daily (6 with naftifine cream, 2% and 6 with naftifine gel, 2%). Subjects had twelve 8 cm2 test application sites demarcated on the upper back. Twenty-five individual sequential strips were obtained from each test site. Of these, 11 sites were dosed once daily with the drug (5.0μL/cm2) for days 1 to 14 and the final site served as the control. On days 15, 29, and 43, a site was stripped to collect the SC in order to process the amount of drug present.

Results: Naftifine was present on all tape strip samples collected over the 28 day period following two weeks of application. Furthermore, the most relevant, deeper tape strip sets reflecting the SC, showed potentially clinically relevant presence of naftifine in the skin for 28-days post-treatment.

Conclusions: Naftifine was present in the tape strips on all sample collection days up to and including four weeks following the last drug application. These findings help explain the progressive improvement in clinical and mycological response rates during the treatment period and for up to four weeks post-treatment in the clinical trials using naftifine.