Fixed-Combination Gels of Adapalene and Benzoyl Peroxide Provide Optimal Percutaneous Absorption Compared to Monad Formulations of These Compounds: Results from Two In Vitro Studies

INTRODUCTION: Adapalene 0.1%/benzoyl peroxide 2.5% (0.1% A/BPO) and adapalene 0.3%/BPO 2.5% (0.3% A/BPO) gels are fixed-combination options for the topical treatment of acne. However, the active compounds of these combinations are also available as monads, to be used in association or as monotherapy. These two in vitro studies determined the effect of different treatment regimens on the percutaneous absorption of adapalene (0.1% and 0.3%) gels and BPO 2.5% gel in ex vivo human skin. METHODS: In vitro percutaneous absorption studies were conducted using full-thickness human skin from six donors. Treatment regimens included the application of 0.1% A/BPO, 0.3% A/BPO, or four free-combination regimens of the monads. Skin samples were incubated for 24 h. Concentrations of adapalene and BPO equivalent (BPO-eq) (i.e. benzoic acid after chemical transformation of BPO) were measured using high-performance liquid chromatography. Comparison of regimens was performed using a bioequivalence criterion (estimated ratio bewteen 0.8 and 1.25). RESULTS: The fixed combination 0.3% A/BPO regimen demonstrated more than three times higher absorption of adapalene versus the fixed-combination 0.1% A/BPO. Based on the bioequivalence acceptance criterion, all four free-combination regimens were different from 0.1% A/BPO and 0.3% A/BPO, with higher adapalene release delivered by the fixed combinations versus the free combinations. For BPO-eq, the results showed that the free-combination regimens where adapalene 0.1% was applied first were different from 0.1% A/BPO, with lower BPO-eq release delivered by these regimens compared to the fixed combination. The regimen adapalene 0.3% for 10 h followed by BPO 2.5% delivered lower BPO-eq release compared to the fixed combination. CONCLUSION: The fixed-combination A/BPO gels provide optimal percutaneous absorption of the active compounds compared to free combinations of adapalene 0.1%, adapalene 0.3%, and BPO 2.5%. The higher concentration of adapalene in the 0.3% A/BPO gel and the resulting higher absorption may explain higher clinical efficacy.