ORLANDO, Fla.—Sevelamer carbonate significantly decreases the bioavailability of oral calcitriol when the two drugs are administered together, but lanthanum carbonate does not, data show.

Investigators at Shire Pharmaceuticals, which makes lanthanum carbonate, conducted an open-label cross-over study that included 41 subjects who received the following treatment regimens in randomized sequences: oral calcitriol alone; oral calcitriol plus lanthanum carbonate; and oral calcitriol plus sevelamer carbonate.

The bioavailability of calcitriol was decreased significantly by 55% when co-administered with sevelamer carbonate but did not change significantly when given with lanthanum carbonate. In addition, the maximum calcitriol serum concentration is significantly reduced when calcitriol is co-administered with sevelamer carbonate, but not lanthanum carbonate.

Continue Reading

“Nephrologists should consider this drug-drug interaction when treating patients who require phosphate binders and oral vitamin D supplementation,” the authors concluded.

The investigators noted that sevelamer has a high affinity for bile salts, and thus may interfere with absorption of fat-soluble molecules such as vitamin D.