[The photostability of antimycotics. 3. Photostability of locally acting antimycotics]

The photochemical stability of a number of topical antimycotic drugs was tested. The light sensitivity decreases in the order naftifine, sulbentine, cloxiquin, tolnaftate and chlorphenesin. A liquid chromatography-mass spectrometry system was used to identify a number of photodegradation products. Light exposure of sulbentine leads to the formation of benzylisothiocyanate. Chlorphenesine solutions undergo photodehalogenation with the formation of varying photodegradation products depending on the solvent used. The photochemical reactions of naftifine are a cis-trans-isomerization and the formation of a dimer product. Drug preparations are also degraded under light exposure in a simulated topical application. Excipients in the drug preparations strongly influence the photodegradation kinetics and the chemical structure of photodegradation products.