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).

Determination of bifonazole and identification of its photocatalytic degradation products using UPLC-MS/MS.

The main goal of the presented work was to investigate the effect of ZnO or/and TiO2 on the stability of bifonazole in solutions under UVA irradiation. To this end, a simple and reproducible UPLC method for the determination of bifonazole in the presence of its photocatalytic degradation products was developed. Linearity was studied in the range of 0.0046-0.15 mg mL-1 with a determination coefficient of 0.9996. Bifonazole underwent a photocatalytic degradation process under the experimental conditions used. Comparative studies showed that combination of TiO2 /ZnO (1:1 w/w) was a more effective catalyst than TiO2 or ZnO with a degradation rate of up to 67.57% after 24 h of irradiation. Further, kinetic analyses indicated that the photocatalytic degradation of bifonazole in the mixture of TiO2 /ZnO can be described by a pseudo-first order reaction. Statistical comparison clearly indicated that the presence of TiO2 /ZnO also affected the stability of bifonazole from a cream preparation after 15 h of UVA exposure (p < 0.05). Ten photodegradation products of bifonazole were identified for the first time and their plausible fragmentation pathways, derived from MS/MS data, were proposed. The main pathway in the photocatalytic transformation of bifonazole in the presence of ZnO or/and TiO2 involves hydroxylation of the methanetriyl group and/or adjacent phenyl rings and cleavage of the imidazole moiety.