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.