Phototoxicity of methoxsalen in various vehicles.

Methoxsalen (8-methoxypsoralen) was used as the photoxic substance in the study of the properties of various vehicles in photoepicutaneous testing. Macrogols as such were relatively poor bases, and positive reactions were seen only occasionally at a concentration of 0.05% methoxsalen. Increasing amounts of water in macrogols brought forth more numerous and stronger reactions. The photoxicity also increased when ethanol was added. The reactions were, however, weaker than to those with aqueous bases. Wool fat and glycerol as vehicles usually reacted in the same way as polyethylene glycols when water was added. An explanation of the mechanism of the changes in the properties of vehicles due to the addition of water/ethanol requires further investigation.