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Concentration‐dependent phototoxicity in trimethylpsoralen bath psoralen ultraviolet A
Author(s) -
Snellman E.,
Rantanen T.
Publication year - 2001
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.1365-2133.2001.04073.x
Subject(s) - phototoxicity , psoralen , confidence interval , ultraviolet a , photosensitivity , puva therapy , medicine , ultraviolet , chemistry , dermatology , psoriasis , biochemistry , dna , physics , quantum mechanics , in vitro
Background Long‐term use of topical trimethylpsoralen (TMP) psoralen bath plus ultraviolet A (bath PUVA) is considered safe with regard to the risk of skin cancer. However, the potential for severe phototoxicity limits its use. Objectives To study the effect of dilution of the TMP bath on the minimal phototoxic dose (MPD). Methods Fifteen volunteers participated in the study. The MPD tests were performed for three TMP concentrations: 0·33 mg L −1 , 0·1 mg L −1 and 0·033 mg L −1 at 2‐week intervals. Geometric UVA dose series increasing by a factor of √2 were used for the testing on the previously unexposed buttock skin. The MPD 72 h was assessed at 72 h from the bath. Results For the highest TMP concentration of 0·33 mg L −1 , the median MPD 72 h was 0·14 J cm −2 (95% confidence interval (CI), 0·10–0·14 J cm −2 ). For the diluted TMP bath concentration of 0·1 mg L −1 , the median MPD 72 h increased to 0·29 J cm −2 (95% CI, 0·2–0·41 J cm −2 ) and for 0·033 mg L −1 to 0·81 J cm −2 (95% CI, 0·57–1·15 J cm −2 ), respectively. Thus, diluting the labelled concentration of 0·33 mg L −1 1 : 10 increased the median MPD 72 h 5·6‐fold. Conclusions With regard to the safety and practicality of the TMP bath PUVA, the lower concentrations of TMP may be of clinical importance, and this needs to be validated in future controlled clinical trials.