Evaluation of PUVA bath phototoxicity
Neumann NJ, Kerscher M, Ruzicka T, Lehmann P
Administration of 8-methoxypsoralen in a dilute bath water solution is an effective therapeutic alternative to its systemic application, avoiding systemic side effects. Although PUVA bath photochemotherapy is now widely used, standardized guidelines are not yet available. Therefore, the aim of our study was to determine the optimal time interval between 8-methoxypsoralen bath and UVA irradiation and the persistence of photosensitivity after PUVA bath treatment. In volunteers the highest photosensitivity was observed following UVA irradiation immediately after PUVA bath. A sharp increase of the minimal phototoxic dose could be demonstrated after only 1 h, indicating a rapid loss of 8-methoxypsoralen activity. Irradiation 2 h after 8-methoxypsoralen bath failed to induce any PUVA erythema. This indicates that the optimal time for UVA irradiation is immediately after the 8-methoxypsoralen bath. In contrast to systemic PUVA therapy, 2 h after PUVA bath therapy, the remaining phototoxicity is minimal, so that no stringent restrictions of the patient's behaviour are needed.