Biopharmaceutics, pharmacokinetics and pharmacology of psoralens

The psoralen derivative 8-methoxypsoralen (8-MOP) and to a lesser extent some other psoralens, including 5-methoxypsoralen (5-MOP) and 4,5',8-trimethylpsoralen (TMP) have acquired a place in the treatment of psoriasis and other dermatoses. They are only active when combined with long-wave ultraviolet light: PUVA therapy (Psoralen plus UVA). Successful PUVA therapy depends on sufficiently high psoralen concentrations coinciding with the time of irradiation. The use of oral or rectal pharmaceutical formulations with 8-MOP dissolved in liquid is preferable to conventional tablets or capsules. Since no formulation of 5-MOP with fast and predictable absorption is available 8-MOP should be preferred in PUVA therapy. The effectiveness of oral TMP is doubtful, because of low serum concentrations, probably due to malabsorption.