The Effect of Simulated Solar UV Irradiation on Tretinoin in Tretinoin Gel Microsphere 0.1% and Tretinoin Gel 0.025%

Topical tretinoin is highly effective and widely used in the treatment of acne vulgaris. Tretinoin gel microsphere 0.1% (TGM)—alone or in combination with erythromycin–benzoyl peroxide (EBP) or clindamycin–benzoyl peroxide (CBP) topical gels—and tretinoin gel 0.025% (TG)—alone or combined with EBP—were exposed to simulated solar UV irradiation to determine the degree of tretinoin photodegradation/isomerization. The investigation revealed that 94% and 84% of the initial tretinoin in the TGM formulation remained stable after 2 and 6 hours, respectively, of simulated solar UV irradiation. When combined with EBP topical gel, 89% and 81% of the initial tretinoin remained stable after 2 and 6 hours, respectively, of exposure to simulated solar UV irradiation; 86% and 80% of the tretinoin remained stable after 2 and 6 hours, respectively, when combined with CBP topical gel. In contrast, only 19% and 10% of the tretinoin remained unchanged after 2 and 6 hours, respectively, of simulated solar UV irradiation of TG. Combined with the EBP topical gel, undegraded tretinoin quantities were further reduced to 7% and 0% at 2 and 6 hours, respectively, with TG. These data suggest that the TGM formulation offers marked protection against tretinoin photodegradation compared with TG, even in the presence of a topical gel containing a potent antibiotic or a strong oxidizing agent. Although simulated solar UV irradiation is not entirely reflective of actual conditions, the results appear to be substantial.