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 applicati on of calcipotriol, but studies are needed to decide how the two treatments should be combined. We studied the effect of UVB after application of calc ipotriol ointment (50 mu g g(-1)) and calcipotriol cream (50 mu g g(-1)) an d 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 c ream was applied randomly on five areas on the back at different time inter vals from UVB irradiation. One area was left untreated as the control. Appl ication times were the evening before, the morning before, 2 h before, imme diately before, and immediately after irradiation. UVB irradiation was admi nistered by TL20W/12 fluorescent tube lamps at increasing doses (20, 251 32 , 40, 50 and 64 mJ cm(-2)) to six subunits of each test area. Clinical asse ssment was performed 24 h after UVB irradiation by a blinded investigator C alcipotriol ointment and cream were applied in 19 and 18 subjects, respecti vely, and erythema was measured for each application time quantified. We fo und that erythemal reactions were significantly smaller when calcipotriol o intment or cream was applied immediately before irradiation compared with a ll other application times. To explain these findings, a vehicle control st udy was performed. No difference in erythema was seen between calcipotriol medication and the vehicle controls. Spectrophotometric analysis of the cal cipotriol cream and ointment showed no UV absorbance in the UVB range. No s igns of photosensitization were noted, In conclusion, the vehicles of the c alcipotriol ointment and cream inhibit the induction of erythema by UVB irr adiation if applied immediately before phototherapy, Consequently, calcipot riol ointment and cream should not be applied directly before UVB irradiati on; however, they map be applied at any time up to 2 h prior to or immediat ely after UVB irradiation. Possible explanations for this sunscreen activit y are discussed.