Endocrinology Division, Department of Medicine, Stony Brook University School of Medicine , Stony Brook, New York 11794-8154, USA.
Thyroid. 2011 May;21(5):483-6. doi: 10.1089/thy.2010.0296.
Calcium carbonate is a commonly used dietary supplement and has been shown to interfere with levothyroxine absorption. However, calcium citrate, which is also used for supplementation purposes, has not been studied previously and calcium acetate, which is used to treat hyperphosphatemia in renal failure, has been reported to show little or no interference with levothyroxine absorption in a retrospective pharmacoepidemiologic study. We aimed to compare the effect of these three calcium formulations on levothyroxine absorption.
The study was conducted in eight healthy, euthyroid adults. We performed single-dose pharmacokinetic studies in which we measured levothyroxine absorption when given alone or when coadministered with calcium carbonate, calcium citrate, or calcium acetate in doses containing 500 mg elemental calcium. Serum thyroxine was measured at intervals over a 6-hour period after ingestion of the study drugs.
Coadministration of each of the three calcium preparations significantly reduced levothyroxine absorption by about 20%-25% compared with levothyroxine given alone.
Contrary to a prior report, our data suggest that calcium acetate interferes with levothyroxine absorption in a manner similar to that seen with calcium carbonate and calcium citrate. Although the effect of calcium is modest compared with some other medications previously studied, hypothyroid patients should be cautioned to take their levothyroxine well-separated from all of these calcium formulations.
碳酸钙是一种常用的膳食补充剂，已被证明会干扰左甲状腺素的吸收。然而，柠檬酸钙也被用于补充，以前没有研究过，醋酸钙用于治疗肾衰竭时的高磷血症，据报道在回顾性药物流行病学研究中，对左甲状腺素的吸收几乎没有干扰或没有干扰。我们旨在比较这三种钙制剂对左甲状腺素吸收的影响。
该研究在 8 名健康、甲状腺功能正常的成年人中进行。我们进行了单次剂量药代动力学研究，当单独给予或与碳酸钙、柠檬酸钙或醋酸钙联合给予时，测量左甲状腺素的吸收，这些剂量含有 500mg 元素钙。在摄入研究药物后 6 小时的间隔内测量血清甲状腺素。
与单独给予左甲状腺素相比，三种钙制剂的联合给药均显著降低了左甲状腺素的吸收约 20%-25%。
与之前的报告相反，我们的数据表明，醋酸钙以与碳酸钙和柠檬酸钙相似的方式干扰左甲状腺素的吸收。虽然与以前研究过的一些其他药物相比，钙的作用较小，但甲状腺功能减退症患者应注意将其左甲状腺素与所有这些钙制剂分开服用。
