Photostability and phototoxicity studies on diltiazem

The photostability of diltiazem was studied in aqueous solutions at different pH values. Firstly, the hydrolysis of the drug to desacetyldiltiazem in alkaline medium was evaluated and then the drug photodegradation under exposure to UVA-UVB radiation (solar simulator) was monitored by HPLC methods. The main photoproduct was isolated and characterized as diltiazem-S-oxide on the basis of the NMR and mass spectra. The HPLC method was also applied to the selective analysis of diltiazem in commercial formulations. Tests on mutagenicity and photomutagenicity of the drug were also carried out using Salmonella typhimurium TA 102 strain. In this testing the drug neither was mutagenic nor toxic.