Pharmacokinetic and pharmacodynamic comparison of two calcium supplements in postmenopausal women

This randomized crossover study compared the single-dose bioavailability an d effects on parathyroid function of two commercially formulated calcium su pplements containing 500 mg of elemental calcium. Twenty-five postmenopausa l women underwent three phases of study wherein they each took a single dos e of calcium citrate with a standard breakfast (as Citracal(R) 250 mg + D), calcium carbonate las Os-Cal(R) 500 + D), or placebo at 8 a.m. Blood sampl es were drawn at baseline and hourly for 4 or 6 hours after each dose. Fast ing and postload urine samples were also collected. Compared with calcium c arbonate, calcium citrate provided a 46% greater peak-basal variation and 9 4% higher change in area under the curve for serum calcium and a 41% greate r increment in urinary calcium. Moreover, the decrement in serum parathyroi d hormone concentration from baseline was greater after calcium citrate. In conclusion, calcium citrate is more bioavailable than calcium carbonate wh en given with a meal. (C)2000 the American College of Clinical Pharmacology .