Serum and urine concentrations of 5-methoxypsoralen after oral administration.

Serum and urine concentrations were measured after oral administration of 5-methoxypsoralen (0.6 mg/kg or I.2 mg/kg) to psoriasis patients. A dose of 0.6 mg/kg resulted in low serum concentrations, but after I.2 mg/kg, much higher serum concentrations were reached. There was much individual variation in the time required for reaching peak serum levels. Minute amounts of unchanged 5-methoxypsoralen were excreted in urine. Much larger amounts were excreted as conjugates.