Norman R. C. Campbell, MD; Brian B. Hasinoff, PhD; Helga Stalts, RN; Babu Rao, MD; Norman C. W. Wong, MD
Campbell N., Hasinoff B., Stalts H., Rao B., Wong N.; Ferrous Sulfate Reduces Thyroxine Efficacy in Patients with Hypothyroidism. Ann Intern Med. 1992;117:1010-1013. doi: 10.7326/0003-4819-117-12-1010
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Published: Ann Intern Med. 1992;117(12):1010-1013.
▪ 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.
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Endocrine and Metabolism, Thyroid Disorders.
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Print ISSN: 0003-4819 | Online ISSN: 1539-3704
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