In vitro human skin study of combined application of pimecrolimus cream and betamethasone 17-valerate

Abstract

Topical calcineurin inhibitors are becoming common therapies for various dermatoses. Combining topical steroids with topical calcineurin inhibitors could potentially accelerate the onset of action, enhance permeation through thicker skin, and reduce the amount of each active medication applied, due to synergistic effects of topical steroids and calcineurin inhibitors. Objective: To investigate the feasibility of co-applying pimecrolimus cream and betamethasone 17-valerate (BMV) in various vehicles. Methods: Five microliters of BMV 0.12% in either foam, ointment, cream, or lotion vehicle was added to a series of glass vials containing 5 mL of pimecrolimus cream 1%. Formulations alone were used individually as controls. Samples were incubated for 0, 2, 4, 6, 8 and 24 hours at either 32°C or 37°C. Drug content was analyzed with HPLC. Permeation through split-thickness human skin (∼0.25 mm) was measured using flow-through diffusion cells. Five microliters of Pimecrolimus cream 1% was applied on the skin membranes, followed 5 minutes later by 5 mL BMV 0.12% either in foam, ointment, or cream vehicle. BMV and pimecrolimus were applied individually as controls. Each combination was tested on three replicate skin sections of at least three human donors. Receptor fluid was collected at 4-hour intervals. At 24 hours after application, the skin was washed and split into epidermis and dermis to measure drug content within these layers. The drug content in samples was measured by HPLC. Results: Pimecrolimus and BMV contents in combination did not show apparent degradation when mixed in different vehicles in vitro after various periods of co-incubation. Permeation of pimecrolimus and BMV will be tested by analyzing the drugs content in the receptor fluid following co-application of pimecrolimus cream and BMV in either foam, ointment, or cream vehicle. Conclusions: Our data show that pimecrolimus and BMV were stable over a period of 24 hours when mixed in various vehicles at either 32°C or 37°C. We will study the permeability of pimecrolimus and BMV when co-applied to skin in various vehicles. The potential synergistic effects of combined application will also be studied.