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Assessment of minimal phototoxic dose following 8‐methoxypsoralen bath: maximal reaction on average after 5 days
Author(s) -
BehrensWilliams S.,
Gruss C.,
GrundmannKollmann M.,
Peter R.U.,
Kerscher M.
Publication year - 2000
Publication title -
british journal of dermatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.304
H-Index - 179
eISSN - 1365-2133
pISSN - 0007-0963
DOI - 10.1046/j.1365-2133.2000.03250.x
Subject(s) - phototoxicity , psoralen , erythema , puva therapy , methoxsalen , medicine , irradiation , dermatology , chemistry , psoriasis , dna , biochemistry , physics , nuclear physics , in vitro
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/cm 2 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/cm 2 ) to day 5 (mean ± SD 1·15 ± 0·63 J/cm 2 ) and started to increase at day 6 (mean ± SD 1·6 ± 0·52 J/cm 2 ). 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.