Methoxsalen Serum Level Variations in Psoralen and Ultraviolet-A (PUVA) Therapy

Abstract

To the Editor.— The weak factor in the present PUVA treatment schedules is not the UV-A component (the irradiation equipment and dosimeters are adequate) but the methoxsalen dose. Even if a fixed dose of methoxsalen is given according to body weight, this does not mean that the serum levels and the skin concentrations are always the same. Day-to-day variations in methoxsalen serum levels can be attributed to different rates of methoxsalen absorption in the gastrointestinal tract. While we know little about the effect of drugs on methoxsalen absorption, we do know that diet can substantially influence methoxsalen absorption and, hence, methoxsalen serum levels.¹ Moreover, many patients are not getting the most out of their PUVA treatments because of the form of methoxsalen being used. Methoxsalen has a low degree of solubility in water, and, therefore, particle size and crystal form can notably influence its bioavailability. Since the methoxsalen available