Purpose: To determine if sucralfate causes malabsorption of L-thyroxine.
Patients and methods: Five healthy volunteers ingested L-thyroxine, 1,000 micrograms, administered orally (1) without sucralfate, (2) with sucralfate, 1 g, and (3) 8 hours after sucralfate, 2 g. The amount of L-thyroxine absorbed was calculated from the peak increase in serum T4 levels within 6 hours of hormone ingestion multiplied by the volume of distribution for the hormone.
Results: Peak absorption of L-thyroxine in the absence of sucralfate was 796 micrograms (95% confidence interval (CI): 515-1,074 micrograms). Coadministration of sucralfate, 1 g, with L-thyroxine reduced thyroid hormone absorption to 225 micrograms (95% CI: 151-299 micrograms) (P = 0.0029 compared with control). Peak hormone absorption was delayed 2 hours by simultaneous sucralfate ingestion. Separation of administered L-thyroxine and sucralfate doses by 8 hours returned hormone absorption to control values. Maximum T3 levels did not differ, regardless of drug regimen, but suppression of thyroid-stimulating hormone (TSH) by L-thyroxine was reduced by coadministration of sucralfate.
Conclusions: Sucralfate causes malabsorption of L-thyroxine, presumably by intraluminal binding of hormone.