Calcipotriol ointment and cream or their vehicles applied immediately before irradiation inhibit ultraviolet B-induced erythema.

Results of ultraviolet (UV) B phototherapy can be improved by the application of calcipotriol, but studies are needed to decide how the two treatments should be combined. We studied the effect of UVB after application of calcipotriol ointment (50 microg g-1) and calcipotriol cream (50 microg g-1) and determined the optimal time of application of calcipotriol when combined with UVB phototherapy (280-350 nm), in a single-blinded randomized vehicle-controlled study of 37 healthy adult volunteers. Calcipotriol ointment or cream was applied randomly on five areas on the back at different time intervals from UVB irradiation. One area was left untreated as the control. Application times were the evening before, the morning before, 2 h before, immediately before, and immediately after irradiation. UVB irradiation was administered by TL20W/12 fluorescent tube lamps at increasing doses (20, 25, 32, 40, 50 and 64 mJ cm-2) to six subunits of each test area. Clinical assessment was performed 24 h after UVB irradiation by a blinded investigator. Calcipotriol ointment and cream were applied in 19 and 18 subjects, respectively, and erythema was measured for each application time quantified. We found that erythemal reactions were significantly smaller when calcipotriol ointment or cream was applied immediately before irradiation compared with all other application times. To explain these findings, a vehicle control study was performed. No difference in erythema was seen between calcipotriol medication and the vehicle controls. Spectrophotometric analysis of the calcipotriol cream and ointment showed no UV absorbance in the UVB range. No signs of photosensitization were noted. In conclusion, the vehicles of the calcipotriol ointment and cream inhibit the induction of erythema by UVB irradiation if applied immediately before phototherapy. Consequently, calcipotriol ointment and cream should not be applied directly before UVB irradiation; however, they may be applied at any time up to 2 h prior to or immediately after UVB irradiation. Possible explanations for this sunscreen activity are discussed.