Cumulative irritancy potential of adapalene cream 0.1% compared with adapalene gel 0.1% and several tretinoin formulations.

Thirty-one subjects (8 males and 23 females; mean age, 49.8 years) were enrolled in a single-center study to assess the irritancy potential of adapalene (Differin cream 0.1% and Differin gel 0.1%) and tretinoin (Avita cream 0.025%, Retin-A cream 0.025%, Retin-A cream 0.05%, Retin-A Micro gel 0.1%, and generic cream 0.025%) as compared with white petrolatum when applied under occlusive conditions. All test materials were applied randomly under occlusion to sites located on the upper area of the subject's back under protective patches. All patches were applied to the same sites unless the degree of reaction to a test product or the adhesive necessitated removal (grade 3). Each test material was applied daily, Monday through Friday, for approximately 24 hours, with the Friday patches left in place over the weekend. Twenty-six of the 31 subjects (84%) completed the study. No subject discontinued because of an adverse event. Five subjects voluntarily discontinued the study early for reasons unrelated to study treatment (4 subject request and 1 lost to follow-up). In the statistical comparison of the 7 test products, the mean cumulative irritancy index of both adapalene cream 0.1% and gel 0.1% was statistically significantly (P<.05) lower than for all of the tretinoin products used and was not significantly higher than the negative control product (white petrolatum).