Photostability of pitavastatin--a novel HMG-CoA reductase inhibitor

The photostability of pitavastatin, an HMG-CoA reductase inhibitor used in the treatment of hypercholesterolemia, was investigated. The sample solution was exposed to UV-A radiation and the photodegradation process was monitored by means of spectrophotometric method and HPLC-DAD. Pitavastatin was shown to be photolabile and its photodegradation reaction followed the first-order kinetics with the rate constant k=3.54 x 10(-4)+/-9.43 x 10(-6)s(-1). The chromatograms revealed the presence of four major photoproducts (PP-1-PP-4). The separated and isolated photolytic products were identified using a mass spectrometer coupled with a time of flight (TOF) analyzer. The main reaction observed during exposure to radiation of pitavastatin was photocyclisation leading to formation of four-ring photoproducts.