Oral calcium tolerance test in extensive psoriasis treated with topical calcipotriol

The vitamin D3 derivative calcipotriol (Daivonex) is an efficient topical treatment of psoriasis. When applied at a dose of about 25 g/week over a mean body surface of 16%, it is not associated with any detectable change in calcium metabolism.

Our purposes were (i) to analyze the effects of calcipotriol on various parameters of calcium metabolism when applied on a large body surface and (ii) to evaluate the usefulness of an oral calcium tolerance test in monitoring psoriatic patients under topical calcipotriol.

In group 1, 10 patients with psoriasis affecting 67.0 +/- 2.7% of total body surface (range 55-80%) were treated with calcipotriol for 6.5 weeks (mean 383 g/month). In group 2, 19 patients with psoriasis involving 15% of body surface were treated with calcipotriol for 9 weeks (mean 105 g/month). In group 3, 7 patients without topical calcipotriol for at least 1 week were given 1.5 micrograms of oral calcitriol for 7 days. An extended survey of blood and urinary parameters of calcium metabolism was performed before and after 45 days of treatment (group 1). Since one of the actions of vitamin D is to stimulate intestinal calcium absorption, an oral calcium-loading test (groups 1, 2 and 3) was done in order to detect more subtle changes possibly induced by calcipotriol.

We did not detect any significant change in various parameters of calcium metabolism in group 1 (large body surface treated) patients. The urinary calcium responses to the oral calcium load were identical to controls in both group 1 (large body surface treated) and group 2 (limited body surface treated), whereas in group 3 (oral calcitriol therapy) an increased urinary calcium response to the calcium load was identified.

No significant changes in calcium metabolism were detectable when calcipotriol was administered once a day over a large body surface with doses up to 100 g/week. The oral calcium tolerance test appears to be a cheap, simple and sensitive test to monitor patients exposed to high doses of calcipotriol as it detects increased intestinal calcium absorption induced by 1.5 micrograms of oral calcitriol.