Sevelamer Carbonate May Impair Calcitriol Bioavailability
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.
“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.