Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism.

TY - JOUR T1 - Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism. AU - Campbell,N R, AU - Hasinoff,B B, AU - Stalts,H, AU - Rao,B, AU - Wong,N C, PY - 1992/12/15/pubmed PY - 1992/12/15/medline PY - 1992/12/15/entrez SP - 1010 EP - 3 JF - Annals of internal medicine JO - Ann. Intern. Med. VL - 117 IS - 12 N2 - OBJECTIVE: To determine whether simultaneous ingestion of ferrous sulfate and thyroxine reduces the efficacy of thyroid hormone in patients with primary hypothyroidism. DESIGN: Uncontrolled clinical trial. SETTING: Outpatient research clinic of a tertiary care center. PATIENTS: Fourteen patients with established primary hypothyroidism on stable thyroxine replacement. INTERVENTION: All patients were instructed to ingest simultaneously, a 300-mg ferrous sulfate tablet and their usual thyroxine dose every day for 12 weeks. RESULTS: After 12 weeks of ferrous sulfate ingestion with thyroxine, the mean level of serum thyrotropin (thyroid stimulating hormone, TSH) rose from 1.6 +/- 0.4 to 5.4 +/- 2.8 mU/L (P < 0.01), but the free thyroxine index did not change significantly. Subjective evaluation using a clinical score showed that nine patients had an increase in symptoms and signs of hypothyroidism; the mean score for the 14 patients changed from 0 to 1.3 +/- 0.4 (P = 0.011). When iron and thyroxine were mixed together in vitro, a poorly soluble purple complex appeared that indicated the binding of iron to thyroxine. CONCLUSIONS: Simultaneous ingestion of ferrous sulfate and thyroxine causes a variable reduction in thyroxine efficacy that is clinically significant in some patients. The interaction is probably caused by the binding of iron to thyroxine. SN - 0003-4819 UR - https://www.unboundmedicine.com/medline/citation/1443969/full_citation L2 - http://www.annals.org/article.aspx?volume=117&amp;page=1010 ER -