Photodegradation studies on lacidipine in solution: basic experiments with a cis-trans reversible photoequilibrium under UV-A radiation exposure.

The photostability of Lacidipine, a dihydropyridine drug used in the treatment of mild and moderate hypertension, was studied in solutions exposed to UV-A radiations. The effects of the solvent (ethanol, acetone, dichloromethane), drug concentration and radiation wavelength on the drug photostability were evaluated. Lacidipine and its photoproducts were separated by a selective liquid chromatographic (HPLC) method, under normal phase conditions (CN-column), using n-hexane:ethanol 97:3 (v/v) as mobile phase, at a flow rate of 2.0 ml/min. The main photodegradation products were isolated and characterised and a photodegradation pathway was proposed for Lacidipine in solution. The cis-isomer and a photocyclic isomer proved to be the main photodegradation products.