Sinecatechins ointment 10% (Veregen®) for genital warts: percutaneous penetration of epigallocatechin gallate concentrations in the stratum corneum collected by adhesive tape stripping method

Dear Editor, Camellia sinensis extract/Sinecatechins/10% ointment is a registered topical therapy for the treatment of external and perianal genital warts, to be applied thrice daily.1 Pharmacokinetic studies elucidating the most optimal frequency of application have not been undertaken, and a less frequent (more convenient) application schedule might also be effective.2, 3 Here, we measured epigallocatechin gallate (EGCG) concentrations, the main C. sinensis extract component, in the stratum corneum (SC) over time after one application. The study was approved by the hospital Ethical Committee (NL57691.018.16). In six healthy volunteers, the ointment was applied on the volar arm, as the skin thickness is comparable to genital skin.4 EGCG was measured in 10 stripped SC layers obtained via adhesive tape stripping at 2, 4, 6, 8, 12 and 24 h after a single application, as described before.5 The amount of SC collected by the tapes was assessed by measurement of the optical density (OD). From the protein amount, the relative SC depth was derived as described previously.5 High-performance liquid chromatography (HPLC) was used to determine the EGCG concentration in tape strips. To compensate for variable amount of SC on the tape, the concentration of EGCG on each tape was normalized for the amount of proteins and expressed as μg EGCG/μg protein. The elimination time (half-life) of EGCG in SC was determined from the curve fitted to the data of EGCG (total mass from 10 tapes) vs. time after application (exponential one-phase decay or linear regression). The difference in the EGCG concentrations between tapes was tested by Wilcoxon matched-pairs signed-rank test. As estimated from the protein amount on the tapes, successive stripping by 10 tapes resulted in removal of approximately half of the SC. EGCG showed a log 2 concentration decrease over 24 h, and approximately a log 1–1.5 decrease with SC depth comparing strip 2 with strips 9 and 10 (data not shown). The available concentration in the SC had approximately decreased after 8 h by 71%, after 12 h by 84% and after 24 h by 98%. There was no significant difference between time points 6 and 8 or 8 and 12 h (Fig. 1). After 24 h, a negligible concentration of EGCG was found. The concentration after 24 h was significantly lower compared to the concentrations at 6 and 8 h (P < 0.05). The estimated half-life was 4.5 h (Fig. 2). In one person, curve fitting could not be carried out; therefore, Fig. 2 is based on five subjects. Epigallocatechin gallate pharmacokinetics in SC can be studied with tape stripping and HPLC. No significant difference in EGCG concentrations was found after 8 and 12 h. Three important factors determine the required application frequency of a therapeutic ointment: the ingredient half-life, the mode of action of the ingredient and the minimum concentration necessary to achieve this action.6 Neither the critical concentration of EGCG required in the SC to induce the inflammatory response is known, nor the required duration.7-9 To conclude, tape stripping in combination with HPLC is a useful method to study the pharmacokinetics of EGCG in the skin. The determination of the 4.5-h half-life in SC after one-time application is an important first step in considering a therapy regimen more convenient than three times daily. Assuming that a continuous local presence of EGCG is required for clinical efficacy, a twice-daily application (with a 12-h interval) might be as effective as a thrice-daily application (with an 8-h interval). A clinical trial comparing different application schedules is required to confirm this conjecture. This work was financially supported by Medigene GmbH, Munich, Germany.