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April 1994

Skin Pigmentation as a Predictor of Minimal Phototoxic Dose After Oral Methoxsalen

Author Affiliations

From the Laboratory of Photobiology, Department of Dermatology, Copenhagen University Hospital, Rigshopitalet (Drs Bech-Thomsen and Wulf), and the Department of Clinical Chemistry, Bispebjerg Hospital (Dr Angelo), Copenhagen, Denmark.

Arch Dermatol. 1994;130(4):464-468. doi:10.1001/archderm.1994.01690040068009

Background and Design:  Twenty-eight subjects were phototested to determine their erythemal responses to oral methoxsalen with UV-A and UV-B irradiation. Skin pigmentation was measured by skin reflectance at 550 and 660 nm before irradiation. The smallest UV radiation dose to produce erythema (minimal phototoxic dose and minimal erythema dose, respectively) was determined. The serum concentration of methoxsalen was measured at the time of UV-A irradiation.

Results:  There was a positive correlation between skin pigmentation and both 72-hour minimal phototoxic dose and 24-hour minimal erythema dose. No correlation was demonstrated between methoxsalen serum concentration and minimal phototoxic dose. The combination of skin pigmentation and methoxsalen level did not give a better prediction of minimal phototoxic dose than skin pigmentation alone.

Conclusions:  Skin pigmentation measurements can be used to predict the minimal phototoxic and erythema doses. Skin pigmentation measurements are easy to perform and should be included in both phototherapy and photochemotherapy to improve the efficiency and reliability of the treatment.(Arch Dermatol. 1994;130:464-468)

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