Possible Interaction: Calcium Carbonate and Thyroxine

“Many commonly used drugs, such as bile acid sequestrants, ferrous sulphate, sucralfate, calcium carbonate , aluminium-containing antacids, phosphate binders, raloxifene and proton-pump inhibitors, have also been shown to interfere with the absorption of levothyroxine.”

“A study of 20 patients receiving long-term levothyroxine replacement therapy indicates that calcium carbonate reduces T4 absorption and increases serum thyrotropin levels [5].”

“ConclusionDelaying CC ingestion even by 6–8 h after taking tablet L-T4 is not entirely satisfactory, unlike liquid or softgel L-T4.”

“ PurposeCalcium carbonate was previously shown to interfere with l-thyroxine absorption.”

“A decrease in the absorption of LT4 is established and clinically significant when administered concomitantly with cholestyramine, colesevelam, lanthanum, calcium carbonate , calcium citrate, calcium acetate, iron sulfate, ciprofloxacin, aluminum hydroxide, sevelamer, or proton pump inhibitors.”

“Furthermore, soy products and several drugs, such as calcium carbonate , bile acid sequestrants, proton pump inhibitors, and ferrous sulfate, may alter L-T4 absorption [7].”

“BACKGROUND Calcium carbonate is a commonly used dietary supplement and has been shown to interfere with levothyroxine absorption.”

“Sevelamer was also found to be associated with significantly higher dosing requirement of thyroid replacement than those on either calcium carbonate or calcium acetate (Z = −3.17, P = 0.001).ConclusionSevelamer (but not calcium acetate) in addition to calcium carbonate appears to interfere with the bioavailability of levothyroxine.”

“After taking a high dose of calcium carbonate (1250 mg three × daily) with levothyroxine , she developed biochemical evidence of hypothyroidism (thyrotropin up to 41.4 mU/L) while remaining clinically euthyroid.”

“CONCLUSIONS: Decreased absorption of levothyroxine when given with calcium carbonate may be particularly pronounced in patients with preexisting malabsorption disorders.”

“DISCUSSION: Concomitant administration of levothyroxine and calcium carbonate often results in levothyroxine malabsorption.”

“OBJECTIVE: To describe a patient with primary hypothyroidism in whom ingestion of levothyroxine with calcium carbonate led to markedly elevated serum thyrotropin concentrations.”

“When levothyroxine was coadministered with 2.0 g of calcium (as calcium carbonate ), the maximum average T4 absorption decreased to 579 microg (57.9% of the dose ingested) at 240 minutes.”