Drugs That Reduce Effectiveness of Levothyroxine

the MPR take:

A study published in the journal Clinical Endocrinology sought to determine which drugs cause the most significant interactions with levothyroxine. A total of 10,999 patients on levothyroxine therapy (mostly female, mean age 58 years) were included in the study. Increases in serum TSH concentration, some clinically significant (>5mU/I), were noted in patients taking concomitant iron, calcium, proton pump inhibitors, and estrogen. Patients taking levothyroxine co-administered with statins saw decreases in TSH concentrations; for some, TSH decreased by 5mU/I. No effect on TSH concentrations was seen with glucocorticoids or H2 receptor antagonists. Clinicians should be aware that drugs often prescribed to patients on long-term levothyroxine therapy may reduce the effectiveness of levothyroxine and that TSH levels should be monitored carefully.

Objective: The aim of this study was to determine the extent of drug interactions affecting levothyroxine, using study drugs often co-administered to patients on long-term levothyroxine therapy. Design: A retrospective population analysis linking biochemistry and prescription data between 1 January 1993 and 31 December 2012 was used.