Effect of Rifampin on Thyroid Function Test in Patients on Levothyroxine Medication

PLoS One. 2017 Jan 12;12(1):e0169775. doi: 10.1371/journal.pone.0169775. eCollection 2017.


Background: Levothyroxine (LT4) and rifampin (RIF) are sometimes used together; however, no clinical studies have assessed the effects of these drugs on thyroid function or the need to adjust LT4 dose.

Methods: We retrospectively reviewed the records of 71 Korean patients who started RIF during LT4 treatment. Clinically relevant cases that required dose adjustment according to the American Thyroid Association (ATA)/American Association of Clinical Endocrinologists (AACE) guidelines were identified, and risk factors of increased LT4 dose were analyzed.

Results: After administering RIF, median serum thyroid-stimulating hormone (TSH) level (2.58 mIU/L, interquartile range [IQR] 0.21-7.44) was significantly higher than that before RIF (0.25 mIU/L, IQR, 0.03-2.62; P < 0.001). An increased LT4 dose was required for 50% of patients in the TSH suppression group for thyroid cancer and 26% of patients in the replacement group for hypothyroidism. Risk factor analysis showed that remaining thyroid gland (odds ratio [OR] 9.207, P = 0.002), the time interval between starting RIF and TSH measurement (OR 1.043, P = 0.019), and baseline LT4 dose per kg body weight (OR 0.364, P = 0.011) were clinically relevant variables.

Conclusions: In patients receiving LT4, serum thyroid function test should be performed after starting RIF treatment. For patients with no remnant thyroid gland and those receiving a lower LT4 dose, close observation is needed when starting RIF and TB medication.

MeSH terms

  • Adult
  • Female
  • Humans
  • Hypothyroidism / drug therapy*
  • Logistic Models
  • Male
  • Middle Aged
  • Odds Ratio
  • Retrospective Studies
  • Rifampin / pharmacology
  • Rifampin / therapeutic use*
  • Risk Factors
  • Thyroid Function Tests
  • Thyroid Gland / drug effects
  • Thyroid Gland / metabolism
  • Thyrotropin / blood
  • Thyroxine / pharmacology
  • Thyroxine / therapeutic use*


  • Thyrotropin
  • Thyroxine
  • Rifampin

Grants and funding

The authors received no specific funding for this work.