Involvement of the N4-oxide group in the phototoxicity of chlordiazepoxide in the rat.

To verify whether or not N4-oxide function is involved in the phototoxicity of chlordiazepoxide (CDZ, Librium), photopharmacology of reduced chlordiazepoxide (RCDZ) lacking the N4-oxide group was carried out and compared to that of CDZ. From the distribution of the 2 compounds in the skin and their UV-spectra in the wavelength region of the UV lamp, doses were calculated to allow the comparison of the photopharmacological effects. Contrary to what has been described for CDZ, no difference was found for RCDZ between irradiated and non-irradiated rats. The discussion leads to the conclusion that the N4-oxide group is responsible for systemic effects reported for phototoxic CDZ.