008 The time‐course of TL‐01 UVB erythema

We examined the characteristics of TL-01 UVB erythema and determined the optimal starting dose prior to TL-01 phototherapy, Twenty-eight subjects were recruited. Eight test sites on each subject's back were irradiated with a TL-01 dose series (50-550 mJ/cm2). Erythema was recorded visually and with a reflectance device at 4, 8, 12, 24, 48 and 72 h in 19 subjects and at 12, 15, 18, 21 and 24 h in nine subjects. Dose-response curves were constructed and the D0.025 (equivalent to the visual minimal erythema dose [MED]) and the maximum slope determined. Erythema was evident at 4 h in the 19 subjects tested. The lowest median MED occurred at 12 h (170 mJ/cm2) and this was significantly lower that at 24 h (median 200 mJ/cm2; P = 0.019). the majority of subjects were at maximal erythema at 12 h (22/28) and 15 h (8/9). MED reading at 24 h (MED24 h) would miss peak erythema in 15/28 subjects. If, as is commonly practiced, 70% of the MED24 h was given, 10/28 subjects would have received a first treatment dose that would be equal to or exceed the lowest MED. If 50% of the MED24 h was given, only 2/28 would develop erythema (P = 0.0078, 95% Cl [10-46.5%]). From the dose-response data, D0.025 at 12 h was significantly lower than at 24 h (P = 0.0019). The slope of the erythemal dose-response curve remained constant from 8 to 48 h. Maximal TL-01 UVB erythema occurs at 12 h. Our data suggest that the optimal first TL-01 treatment dose is 50% of the MED24 h.