Skin photosensitizing and Langerhans' cell depleting activity of topical (bath) PUVA therapy: comparison of trimethylpsoralen and 8-methoxypsoralen.

The skin photosensitizing and Langerhans' cell (LC) depleting effects of a single bath PUVA exposure were studied in 22 healthy young volunteers. The photosensitizing effect of bathing for 15 min in a 0.2 mg/1 trioxsalen-water solution was about 30 times as great as a similar treatment in an equipotent methoxsalen solution. The skin erythema induced by methoxsalen bath PUVA peaked on day 2 and diminished thereafter, whereas the trioxsalen reaction showed a broad plateau on days 2-5 after the irradiation. A reduction in LC density to about 30-40% of the starting value was seen in both trioxsalen and methoxsalen bath PUVA treated skin sites on day 4 after irradiation, and low or diminishing LC counts prevailed until day 10-11. The amount of UVA needed to produce a similar degree of LC depletion was 15-30 times as great in the case of methoxsalen, compared with trioxsalen. A perceptible erythema reaction, however, was, not a prerequisite for a reduction in LC density.