Single layer dermal patch: skin accumulation assessed by tape stripping

The aim of this work was to assess the lidocaine skin accumulation after application of single-layer dermal patches, compared to a commercial gel formulation. The tape stripping technique was used. The model drug was lidocaine hydrochloride, applied at the dose of 0.3 mg/cm2 as lidocaine base. Methods. Lidocaine containing patches were applied on the forearm of 6 volunteers for 30 min. (both sex, 24-27 years old), in the presence or absence of iontophoresis. After removal of the patch, or of the excess formulation, the skin was submitted to tape stripping. Tapes were extracted with acetonitrile: pH 4 buffer (14: 86) and lidocaine content was determined by HPLC. In the current assisted experiments, anodal iontophoresis was applied (current density 0.5 mA/cm2 for 30 min.). Results. The results obtained show that lidocaine accumulated in human stratum corneum after single-layer patch application. Drug concentration in skin strips was higher in the more superficial layers and decreased in the deeper layers. The total amount of lidocaine recovered in the tape strips was 7.97 +/- 0.84 and 4.78 +/- 0.78 mcg per mg of stratum corneum for patch and commercial gel, respectively. The application of the patch without water, was less effective, giving rise to a drug content of 2.44 +/- 0.61 mcg/mg. When iontophoresis was applied on the patch (current density 0.5 mA/cm2 for 30 min.), the amount recovered was 13.07 +/- 0.85 mcg/mg. Conclusions. The single-layer dermal patches show higher lidocaine accumulation with respect to reference gel formulation, when compared in vivo using the tape stripping technique. The application of current directly on the patch further increased the amount of drug recovered in the stratum corneum