Isolation and structure elucidation of photodegradation products of fexofenadine.

The photostability of the antihistamine fexofenadine hydrochloride is described. The stress studies revealed the photostability of the drug as the most adverse stability factor. The main photodegradation products were isolated and its structures were elucidated by 1H, 13C, COSY, HSQC, HMBC NMR and mass spectrometry techniques. The drug was exposed to UVC light at 254 nm in methanolic solutions and the degradation was followed by HPLC and TLC. The photostability of fexofenadine tablets was studied and the same degradation products were observed. The two photodegradation products isolated were characterized as the isopropyl derivative, obtained by decarboxilation of fexofenadine, and a benzophenone compound, which was obtained by rearrangement of aromatic rings and oxidation reactions. The results show the importance of appropriate light protection during the drug development process, storage and handling.