The impact of ZnO and TiO2 on the stability of clotrimazole under UVA irradiation: Identification of photocatalytic degradation products and in vitro cytotoxicity assessment

In order to ensure the safe and effective use of pharmaceutical products especially for topical administration photostability testing is necessary. The current paper presents an in-depth analysis of the stability of one of the most common antifungal agents, namely clotrimazole. Clotrimazole has proven to be stable under UVA irradiation in applied experimental conditions, but the presence of catalysts such as ZnO and TiO₂ has contributed significantly to the degradation of this compound. The findings indicate that its photocatalytic degradation reactions followed the pseudo first-order kinetics with rate constant depending on the pH and the used solvent. Using LC-MS/MS, 14 presumable degradation products of clotrimazole were identified and the plausible transformation pathways were proposed. The in vitro cytotoxicity risk evaluation based on photostability of clotrimazole was also performed using the Human skin fibroblast cell line (BJ) ATCC™ CRL-2522. There was no statistically significant difference between cells viability in all analyzed combinations of clotrimazole, TiO₂/ZnO, and UVA irradiation (p<0.05).