title: Minimal phototoxic dose (MPD) measurements for topical photochemotherapy using a semiautomated MPD tester.
abstract: 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).
  
  
  OBJECTIVE
  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.
authors.affiliation: Department of Dermatology, Aneurin Bevan Health Board, St Woolos Hospital, Newport, U.K.
authors.forename: D
authors.initials: D
authors.lastname: Al-Ismail
authors.forename: C
authors.initials: C
authors.lastname: Edwards
authors.forename: O
authors.initials: O
authors.lastname: Al-Ofi
authors.forename: A V
authors.initials: AV
authors.lastname: Anstey
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008730:Methoxsalen / Q000008:administration & dosage; D008875:Middle Aged; D011701:PUVA Therapy / Q000295:instrumentation* / Q000379:methods; D017319:Photosensitizing Agents / Q000008:administration & dosage; D011446:Prospective Studies; D011565:Psoriasis / Q000188:drug therapy*; D011829:Radiation Dosage; D055815:Young Adult
chemical_list: D017319:Photosensitizing Agents; D008730:Methoxsalen