The effects of topical calcipotriol on systemic calcium homeostasis in patients with psoriasis.
2015-11-19T08:50:57Z (GMT) by
Calcipotriol is a new and effective topical treatment for chronic plaque psoriasis vulgaris. It is an analogue of calcitriol (1,25 dihydroxyvitamin D - the active metabolite of vitamin D), and so has the potential to affect systemic calcium metabolism even when used topically. Animal studies indicate that parenteral calcipotriol has a weaker effect on systemic calcium homeostasis than calcitriol. Extensive clinical trials using relatively small amounts of calcipotriol (50mg/g) ointment (on average 30-40g/wk) detected no effect on serum calcium in vivo provided that the recommended maximum weekly dose of 100g was not exceeded. Cases of hypercalcaemia from calcipotriol ointment have been reported, both after excessive use and in relation to manufacturers recommendations. Short wave ultraviolet light (UVB) is commonly used to treat psoriasis in combination with topical agents such as dithranol and tar. The use of calcipotriol in combination with UVB is becoming common practice. UVB initiates synthesis of vitamin D in the skin and therefore might enhance the calciotropic effects of calcipotriol when used in combination. The aims of this study were to detect any alteration of calcium homeostasis in patients treated with topical calcipotriol, to identify the mechanism(s) of any detected effects and to determine whether the addition of UVB would enhance those effects. In summary, we have confirmed that topical calcipotriol does have an effect on systemic calcium homeostasis. Intestinal absorption of calcium, and probably phosphate, is increased, when large doses are applied (up to 360g of the 50mg/g ointment per week). Serum calcium and phosphate rise while serum PTH and 1,25 dihydroxyvitamin D3 levels fell. Urinary excretion of calcium and phosphate are increased. The suppressive effects on PTH and endogenous 1,25 dihydroxyvitamin D3 levels may be due to direct inhibition by calcipotriol as well as indirect effects of rising serum calcium and phosphate. At the upper limit of the recommended dose (100g/wk), calcipotriol has a small but measurable effect on systemic calcium homeostasis as manifested by a small rise in 24h urine calcium and serum ionized calcium. These changes are probably not of clinical significance. The addition of short wave ultraviolet light has no additive effect on systemic calcium homeostasis at recommended doses.