An intraindividual comparative study of psoralen-UVA erythema induced by bath 8-methoxypsoralen and 4, 5', 8-trimethylpsoralen.
BACKGROUND
Limited work has been conducted on the characteristics of topical trimethylpsoralen (TMP) psoralen-UVA (PUVA) erythema.


OBJECTIVE
We sought to determine the time-course and dose-response characteristics of erythema induced by topical TMP, and to compare these parameters with those for topical 8-methoxypsoralen (MOP) within patients.


METHODS
After photosensitization of one forearm with topical TMP, test sites were exposed to a UVA dose series. The procedure was repeated on the other forearm using 8-MOP solution. Erythema was assessed visually and with a reflectance instrument every 24 hours for 7 days.


RESULTS
TMP PUVA erythema followed a similar time course to 8-MOP PUVA erythema. The majority of patients were at maximal erythema at or beyond 96 hours. TMP PUVA had a significantly steeper dose-response curve at 48, 72, and 96 hours compared with 8-MOP PUVA.


CONCLUSIONS
On the basis of these data, the optimal time to read the TMP minimal phototoxic dose is 96 hours. In view of the steeper dose-response curve for TMP PUVA, a lower UVA incremental regimen should be considered compared with that for 8-MOP PUVA.
Man
Irene
I
Photobiology Unit, Department of Dermatology, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland.
McKinlay
Jayne
J
Dawe
Robert S
RS
Ferguson
James
J
Ibbotson
Sally H
SH
D000328:Adult; D004305:Dose-Response Relationship, Drug; D004890:Erythema / Q000139:chemically induced*; D005260:Female; D006801:Humans; D008297:Male; D008730:Methoxsalen / Q000008:administration & dosage / Q000009:adverse effects*; D008875:Middle Aged; D011701:PUVA Therapy / Q000379:methods; D013997:Time Factors; D014307:Trioxsalen / Q000008:administration & dosage / Q000009:adverse effects*
D008730:Methoxsalen; D014307:Trioxsalen