Premium
Minimal phototoxic dose ( MPD ) measurements for topical photochemotherapy using a semiautomated MPD tester
Author(s) -
AlIsmail D.,
Edwards C.,
AlOfi O.,
Anstey A.V.
Publication year - 2013
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 - 10.1111/bjd.12395
Subject(s) - puva therapy , erythema , medicine , psoralen , dermatology , ultraviolet a , phototoxicity , psoriasis , chemistry , dna , biochemistry , in vitro
Summary Background The traditional method of assessing minimal phototoxic dose ( MPD ) prior to photochemotherapy with psoralen–ultraviolet A ( PUVA ) is inconvenient and cannot directly determine PUVA start doses. A handheld minimal erythema dose UVB tester can be modified by fitting a TL ‐10 UVA compact fluorescence lamp ( CFL ). Objectives To determine whether MPD testing is possible with a CFL and to calculate a fixed factor to convert observed MPD to PUVA ‐equivalent MPD . Methods Patients had two sets of MPD tests performed on symmetrical, contralateral sites on the lower back. MPD test results from a panel of PUVA lamps were compared with MPD from the modified handheld tester. Additionally, a questionnaire survey was completed by 43 U.K. phototherapy units to assess routine practice concerning MPD testing prior to PUVA therapy. Results Thirty‐seven patients with psoriasis were recruited. Boston phototypes in the 31 with conclusive MPD reactions were: I, four; II, 11; III, 12; and IV, four. The handheld MPD results were linearly related to the PUVA panel MPD results as follows: PUVA MPD = 0·48 × handheld MPD + 0·17 J cm −2 . The measured PUVA MPD was 0·48 of the handheld MPD , not 0·15 as predicted by the published PUVA action spectrum. Conclusions The modified MPD tester is a convenient and safe method for PUVA MPD testing, overcoming many problems of the ‘traditional method’. The difference between the PUVA and TL ‐10 lamps was lower than predicted from published studies. This suggests that formal re‐evaluation of the erythema action spectrum for PUVA is now needed.