Photodegradation products of sulphonamide-derived oral antidiabetics and diuretics are not phototoxic in vitro.

The oral antidiabetics glibenclamide and glipizide, and the diuretics bendroflumethiazide and furosemide, all sulphonamide derived drugs, were investigated in vitro for phototoxic properties. Irradiation with broad-band UV induced phototoxic inhibition of colony forming ability in cell cultures. During irradiation, the substances lost one absorption maximum in the UVA region, demonstrated by UV spectroscopy. These findings correlate well with the UV applied, the action spectrum being in the UVA region. Photoproducts detected during and after irradiation showed a decomposition of the substances due to ionization and fragmentation. Incubation of these preirradiated drugs with the cell cultures revealed no phototoxic effects.