Effect of UV-B erythema of psoralen, trimethylpsoralen, and 8 methoxypsoralen.

The MED for UV-B was measured 2 h and 24 h after oral intake of Psoralen (P) 0.49 mg/kg in 10 healthy volunteers. MED was increased when UV exposure had taken place 2 h after intake. The same increase was observed after 0.24 mg/kg and 0.98 mg/kg, with a non-significant dose dependence. This effect was not detectable when UV exposure had taken place 24 h after oral intake of the drug. In a second experiment the effects of oral intake of both trimethylpsoralen (TMP) and 8 Methoxypsoralen (8 MOP) mg/kg, were assessed in 29 subjects. While TMP increased MED when taken 2 h before UV exposure (p less than 0.001), 8 MOP had the opposite effect (p less than 0.01). TMP effect was observed mainly in fair-haired people (p less than 0.05) and 8 MOP effect mainly in females (p less than 0.05).