RESUMO
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.
Assuntos
Metoxaleno/metabolismo , Disponibilidade Biológica , Cápsulas , Ensaios Clínicos como Assunto , Cristalização , Humanos , Metoxaleno/administração & dosagem , Metoxaleno/efeitos adversos , Terapia PUVA , Psoríase/tratamento farmacológico , Psoríase/metabolismo , SoluçõesRESUMO
A patient with epilepsy and psoriasis in phenytoin therapy was treated with PUVA with no effect at all. The PUVA treatment failure was demonstrated as being due to abnormally low serum levels of 8-methoxypsoralen (8-MOP) during phenytoin therapy, while normal serum levels of 8-MOP were observed after phenytoin was discontinued. The effect is probably due to an induction of the hepatic enzyme system by phenytoin, leading to an increased metabolism of 8-MOP. Other drugs with hepatic enzyme inducing properties might possibly also interfere with psoralen metabolism with further consequences for PUVA therapy.
