Different photodegradation behavior of barnidipine under natural and forced irradiation

An in depth study on photodegradation of barnidipine, a new 1,4-dihydropyridine antihypertensive drug, was performed by exposing the drug to natural and stressing light irradiation. A different degradation process and distribution of photoproducts under different light sources and irradiation power were demonstrated. Degradation kinetics, reactive excited states involved, transient species and photoproducts generated were investigated. Exposure of barnidipine to forced irradiation caused a complex degradation pathway. Kinetics of this process was studied by HPLC and spectrophotometry, demonstrating the formation of several by-products. In contrast, the drug, under direct or indirect sunlight, underwent oxidation generating the pyridine derivative as the main photodegradation product, according to most of the drug congeners. HPLC and derivative spectrophotometric methods were defined for the simultaneous assay of the drug and its pyridinic by-product, useful as a routine control method of the drug formulations.