title: Erythema action spectrum of topical 8-methoxypsoralen-sensitized skin re-evaluated: implications for routine clinical practice.
abstract: BACKGROUND
  Published methodology used to determine psoralen plus ultraviolet A (PUVA) erythemal action spectrum does not reflect current clinical practice for psoralen sensitization. We re-evaluated the PUVA action spectrum using aqueous 8-methoxypsoralen (8-MOP) 2·6 mg L(-1) as used routinely in current clinical practice.
  
  
  OBJECTIVE
  To determine the UVA erythema action spectrum of topical 8-MOP-sensitized normal skin.
  
  
  METHODS
  Twenty healthy volunteers with skin phototypes I-V were recruited. Forearms were psoralen-sensitized at 37 °C for 10 min. Six UVA irradiations at 10-nm intervals between 325 and 375 nm were randomly allocated to forearm sites and were applied using a 10-nm bandwidth irradiation monochromator. The visual minimal phototoxic dose (MPD) was recorded on each site at 96 h.
  
  
  RESULTS
  Volunteer Boston phototypes were: I, n = 2; II, n = 6; III, n = 6; IV, n = 5 and V, n = 1. The mean MPD (J cm(-2) ) for all subjects at each wavelength was as follows: 325 nm, 0·64 (SD 0·37); 335 nm, 0·80 (SD 0·58); 345 nm, 0·96 (SD 0·55); 355 nm, 1·50 (SD 0·85); 365 nm, 2·19 (SD 0·90); and 375 nm, 2·89 (SD 1·06). Therefore, the relative sensitization at each wavelength (erythemal action spectrum) was: 1, 0·83, 0·67, 0·43, 0·29 and 0·22. There were significant differences between the PUVA erythemal effectiveness at different wavelengths but none between skin types.
  
  
  CONCLUSIONS
  This study has established the erythemal action spectrum for bath/soak PUVA therapy as is currently performed. In all volunteers, the peak sensitivity was at 325 nm. All volunteers showed a similar trend across the wavelengths studied irrespective of skin type. The determination of the action spectrum for PUVA-induced erythema is important as it permits reliable estimates of erythemal efficacy of any UVA source where the emission spectrum of the lamp is known or can be measured.
authors.affiliation: Department of Dermatology, St Woolos Hospital, Aneurin Bevan University Health Board, Newport, NP20 2UB, U.K.|Cardiff University, Heath Park, Cardiff, CF14 4XN, U.K.
authors.forename: D
authors.initials: D
authors.lastname: Al-Ismail
authors.affiliation: Department of Dermatology, St Woolos Hospital, Aneurin Bevan University Health Board, Newport, NP20 2UB, U.K.
authors.forename: C
authors.initials: C
authors.lastname: Edwards
authors.affiliation: Cardiff University, Heath Park, Cardiff, CF14 4XN, U.K.|Department of Dermatology, Ysbyty Gwynedd, Betsi Cadwaladr University Health Board, Bangor, LL57 2PY, U.K.
authors.forename: A V
authors.initials: AV
authors.lastname: Anstey
mesh_terms: D000067549:Action Spectrum; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D017484:Dermatitis, Phototoxic / Q000209:etiology; D004307:Dose-Response Relationship, Radiation; D004890:Erythema / Q000139:chemically induced*; D005260:Female; D005542:Forearm; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008730:Methoxsalen / Q000008:administration & dosage / Q000009:adverse effects*; D008875:Middle Aged; D011701:PUVA Therapy / Q000009:adverse effects*; D017319:Photosensitizing Agents / Q000008:administration & dosage / Q000009:adverse effects*; D055815:Young Adult
chemical_list: D017319:Photosensitizing Agents; D008730:Methoxsalen