Effects of topical calcipotriol on calcium metabolism in psoriatic patients: comparison with oral calcitriol.

The analogue of calcitriol, calcipotriol (MC 903, Daivonex) has been proven effective in the treatment of psoriasis, when given topically. However, the possible influence of cutaneously absorbed MC 903 on calcium metabolism is still unclear. We evaluated various parameters of calcium metabolism in 17 psoriatic patients treated for 5.4 +/- 2.3 (mean +/- SD) weeks with MC 903, on 16 +/- 6% of the body surface. The dose administered (100 g of Daivonex corresponding to 5 mg of MC 903) decreased the PASI score by 40.9 +/- 20.0% (p less than 0.001). Among these patients, 12 were studied before and after MC 903 therapy. In none could be detected any change in protein-adjusted calcium, ionized Ca, plasma levels of creatinine, alkaline phosphatase, osteocalcin, intact parathyroid hormone (PTH), calcidiol and calcitriol, or in daily or fasting urinary excretion of Ca or cAMP. After an MC-903-free period, 9 patients received 1.5 micrograms/day of calcitriol orally for 7 days. Whereas this treatment did not control the skin relapse in most of the patients, it induced a significant increase in plasma levels of protein-adjusted Ca and calcitriol, and in 24-hour urinary Ca excretion, as well as a significant fall in PTH as compared with pretreatment values. These results indicate that 150 micrograms/day of MC 903, despite a possible 1% absorption, i.e. a systemic dose of 1.5 micrograms, did not produce any detectable alteration of Ca metabolism, whereas an equivalent dose of oral calcitriol was associated with significant changes. The threshold dose of topical calcipotriol that might induce alterations similar to 1.5 micrograms/day of oral calcitriol remains to be evaluated.