Reduction in 8-methoxypsoralen immersion time alters the erythemal response to bath PUVA.
Topical psoralen plus ultraviolet A (PUVA) using 8-methoxypsoralen (8-MOP) bath solution is a well established and effective treatment in dermatology. The standard immersion time in the UK is 15 min, but a shorter bathing period could potentially increase treatment convenience. In order to examine the effect of reduction in immersion time on skin phototoxicity, we compared the erythemal response to UVA following 5 min and 15 min psoralen baths. The study was performed on the forearm skin of 7 healthy volunteers using an 8-MOP psoralen concentration of 2.6 mg/l. One forearm of each volunteer was soaked for 15 min and the other for 5 min, followed by immediate irradiation with a series of 10 doses of broadband UVA ranging from 0.1 J/cm2 to 6.9 J/cm2. At 72 h, the minimal phototoxic doses (MPDs) were noted and erythema readings (erythema index) were taken in triplicate with a reflectance instrument. The median MPD following 5 min immersion was 1.7 (range 0.7-2.7) J/cm2 compared with 1.0 (range 0.4-1.7) J/cm2 after 15 min treatment, with no significant difference. However, the mean slope of erythema dose-response on the 15-min treated side was significantly steeper than on the 5-min treated side, 0.036 and 0.021 respectively, P < 0.05. Hence, this preliminary work shows that reducing 8-MOP immersion time to 5 min reduces the erythemal response to UVA. It will clearly be necessary to examine the effect of a shortened immersion period on disease clearance before considering such a change to the topical PUVA regime.
Azurdia
R M
RM
Department of Dermatology, Royal Liverpool University Hospital, UK.
Dean
M P
MP
Rhodes
L E
LE
D000328:Adult; D001494:Baths; D004890:Erythema; D005260:Female; D005542:Forearm; D006801:Humans; D016014:Linear Models; D008297:Male; D008730:Methoxsalen / Q000494:pharmacology*; D011701:PUVA Therapy; D018709:Statistics, Nonparametric; D013997:Time Factors
D008730:Methoxsalen