IngentaConnect Assessment of minimal phototoxic dose following 8-methoxypsoralen...

Authors: Behrens-Williams, S.¹; Gruss, C.²; Grundmann-Kollmann, M.; Peter, R.U.¹; Kerscher, M.¹

Source: British Journal of Dermatology, Volume 142, Number 1, January 2000 , pp. 112-115(4)

Abstract:

An essential procedure before starting bath psoralen ultraviolet (UV) A (PUVA) photochemotherapy is the evaluation of the minimal phototoxic dose (MPD), which is traditionally assessed 3 days after irradiation. However, there are no controlled studies supporting the 72 h peak of bath-PUVA erythema. The aim of this study was therefore to determine the exact time course of the erythematous reaction in human skin following bath-PUVA. For this purpose, the skin of 10 volunteers was exposed to 0·5-3·0 J/cm² UVA directly after a 20-min 8-methoxypsoralen bath (0·5 mg/L, 37 °C). At 24, 48, 72, 96, 120 and 144 h (1-6 days) after irradiation, the MPD and the erythema sum score (ESS) were determined in each subject. The results showed a maximal erythematous reaction on average 5 days after irradiation. The mean MPD gradually decreased from day 2 (> 3·0 J/cm²) to day 5 (mean ± SD 1·15 ± 0·63 J/cm²) and started to increase at day 6 (mean ± SD 1·6 ± 0·52 J/cm²). The mean ± SD ESS correspondingly increased from day 2 (0 ± 0) to day 5 (10·5 ± 3·7) with a decrease at day 6 (7·5 ± 3·1) (difference between day 3 and beyond statistically significant at P < 0·05). As our study indicates a maximal erythematous reaction to the bath-PUVA up to 5 days after irradiation, the traditional MPD assessment at 3 days generates a risk of phototoxic side-effects within the phototherapy course by underestimating the phototoxic effect in some patients. These findings contribute towards a more defined understanding of the kinetics of the phototoxic reaction in bath-PUVA therapy.

Keywords: 8-methoxypsoralen; bath-PUVA therapy; erythema sum score; minimal phototoxic dose; time course

Document Type: Research article

DOI: 10.1046/j.1365-2133.2000.03250.x

Affiliations: 1: University of Ulm, 2: University of Regensburg and

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Assessment of minimal phototoxic dose following 8-methoxypsoralen bath: maximal reaction on average after 5 days