Photolability and photohemolytic studies of fibrates

Fenofibrate (1), gemfibrozil (2), clofibric acid (3), benzafibrate (4) and clofibrate (5) were found to be photolabile by UV-B (290-320 nm) light under aerobic conditions. The drugs 1, 2, 3 and 4 were phototoxic in vitro when examined by the photohemolysis test both under oxygen and argon atmosphere, although the photohemolysis rate was markedly lower under anaerobic conditions. Based on the inhibition of this process upon addition of butylated hydroxyanisole (BHA) and reduced glutathione (GSH), a radical chain (type I) mechanism appears to operate. Inhibition was seen in the presence of sodium azide (NaN3) and 1,4-diazabicyclo[2.2.2]octane (DABCO) as also in D2O induced-photohemolysis. No photohemolysis was evident for clofibrate (5) under these conditions. In summary, fenofibrate, gemfibrozil, clofibric acid and bezafribrate are phototoxic in vitro. This behavior can be explained through the involvement of free radicals, singlet oxygen and stable photoproducts.