Phototoxicity of topical trioxsalen

The phototoxic properties of topical trioxsalen preparations were studied in 73 test subjects. A W/O emulsion base was superior to petrolatum, O/W emulsion, double emulsion and carbowax. The optimal interval between application of the drug and UVA irradiation varied between 40 and 60 min for both cream and ointment bases. An occlusive dressing greatly enhanced the phototoxic effect of the drug. The skin lost photosensitivity in 4 hours when the preparations were removed from the skin 45 min after the application. For clinical use a proper concentration of trioxsalen in emulsion bases was 0.01-0.1%. Both W/O and O/W emulsion bases with 0.01% trioxsalen locally applied gave moderate or good clinical results in 16 psoriatics and in 4 patients with lichen planus, W/O emulsion being better in this respect.