Further Studies Demonstrating an Increased Erythemal Threshold Following Oral Methoxsalen

Abstract

The use of methoxsalen or 8-methoxypsoralen to augment the normal skin response to ultraviolet light has been intensively studied in recent years. An extensive symposium on psoralens and radiant energy was published in a supplement to this journal in February, 1959 (1). Included in that issue was a report by Imbrie,et al. on increased erythemal threshold five weeks after a single exposure to sunlight and ingestion of 30 mg. of methoxsalen (2). In an experimental group of eight young women, it was shown that nearly twice as much ultraviolet exposure was necessary to produce an erythema on the methoxsalen treated skin as was needed to produce a comparable amount on the control area. However, these results were much more impressive than were those obtained on men receiving 20 mg. of methoxsalen with repetitive solar exposures in Idaho and Arizona (3). Because of differences in drug dose, geographic location and sex, further experiments were required to explain the differences. This report concerns a larger series of males to reaffirm the magnitude of the protective effect and to investigate possible sex differences in response to this drug.