Bioavailability study of two different 8-methoxypsoralen (8-MOP) preparations in patients receiving PUVA therapy

A bioavailability study was performed with a pill containing microcrystalline 8-MOP and a soft gelatine capsule containing dissolved 8-MOP in 35 patients receiving PUVA treatment. Peak plasma levels were almost doubled after ingestion of the capsule preparation in comparison with those recorded from the pill takers. The pharmaceutical formulation of 8-MOP preparations is of decisive importance for the bioavailability of the drug. Variations in degree of absorption from different 8-MOP preparations and the existence of a metabolic first-pass effect probably explain the great inter-patient variability in therapeutic response. It is therefore advisable to individualize the dose of 8-MOP, primarily in slow responders, with the aim of obtaining a faster clearance but also to reduce the amount of UVA light involved.