Problems with commercial formulations of 8-methoxypsoralen

Plasma concentrations of 8-methoxypsoralen were measured in 8 psoriatic patients after administration of two commercial solid formulations and of an 8-methoxypsoralen solution. Systemic availability as measured by the area under the concentration versus time curve was much higher for the solution than for the two commercial formulations. For the solid formulations, a large inter- and intraindividual variation in plasma concentrations was found and in many cases no plasma levels could be measured. Administration of the solution gave always more reproducible plasma concentrations in function of time.