The effects of topical calcipotriol on systemic calcium homeostasis in patients with chronic plaque psoriasis

Background: Calcipotriol is an effective treatment of chronic plaque psoriasis. We have previously demonstrated that it has a small effect on systemic calcium homeostasis even at recommended doses. Objective: We attempted to determine the mechanism of the effect of calcipotriol on sytemic calcium homeostasis so we could assess the possible consequences of long-term use. Methods: Sixteen patients with extensive chronic plaque psoriasis were hospitalized and treated with high-dose topical calcipotriol. Up to 360 gm of calcipotriol (50 @mg/gm) ointment was applied per week for 2 weeks under controlled conditions. Results: There was a dose-dependent rise in intestinal absorption of calcium. No effect on bone turnover was demonstrated over this short period. Five patients became hypercalcemic, and there was a dose-dependent rise in serum total adjusted calcium, serum ionized calcium, serum phosphate, urine calcium, and urine phosphate. There was a dose-dependent fall in serum parathyroid hormone and serum 1,25 dihydroxyvitamin D"3. Conclusion: Calcipotriol exerts its effects on systemic calcium homeostasis by increasing intestinal absorption of calcium and probably phosphate. This results in suppression of parathyroid hormone and 1,25 dihydroxyvitamin D"3. (J Am Acad Dermatol 1997;37:929-34.)