Proton-Pump Inhibitors Inhibit Absorption of Levothyroxine in Tablet Form

Studies have shown that gastric acidity enhances the dissolution of levothyroxine tablets. Thus, proton-pump inhibitors (PPIs), which suppress gastric acid secretion, might be expected to inhibit absorption of levothyroxine delivered as a tablet, but not as liquid.

To examine this issue, Italian researchers identified 24 patients who took both levothyroxine tablets and a PPI daily and whose thyroid-stimulating hormone (TSH) levels were around the upper limit of normal (mean level, 4.1 mU/L). All patients were switched from levothyroxine in tablet form to the same dose in an oral solution (while PPIs were continued), and TSH was remeasured 8 weeks later. After the switch, the mean TSH level fell markedly, to 0.9 mU/L.