Although an in vitro study showed binding of L-thyroxine by sucralfate [1], a later study showed that sucralfate did not interfere with in vivo absorption of replacement L-thyroxine in patients with hypothyroidism [2]. After encountering such a patient receiving replacement L-thyroxine who experienced a decrease in serum thyroxine (T₄) index and a dramatic increase in serum thyrotropin after starting treatment with sucralfate, we studied the effect of sucralfate on L-thyroxine absorption.

After obtaining informed consent and baseline tests, nine patients with primary hypothyroidism were randomly assigned to treatment with sucralfate, 1 g 4 times daily or placebo, one capsule 4 times daily. The mean age was 37 years (range, 20 to 57 years), and the mean daily dose of L-thyroxine was 133 µg (range, 75 to 200 µg). Thyroid tests were obtained after 4 weeks of treatment. Therapy was discontinued for 2 weeks, and the patients then crossed over to the other study medication for 4 weeks. Both patients and investigators were masked to treatment and test results. All patients remained on their starting dose of L-thyroxine throughout the study. The results are shown in Table 1.

When compared with placebo, treatment with sucralfate produced a modest decrease in the serum T₄ index (P = 0.038) and an increase in serum thyrotropin (P = 0.097) that was not statistically different. Only one patient treated with sucralfate developed an elevated serum thyrotropin level, and she also had an elevated thyrotropin value while receiving placebo, suggesting that she was not taking her medications reliably. Thus, our data suggest that sucralfate does not have a major effect on L-thyroxine absorption. However, because of the potential for a decrease in the serum T (₄) index, thyroid function tests should be monitored during concomitant therapy with L-thyroxine and sucralfate.