title: Effect of Rifampin on Thyroid Function Test in Patients on Levothyroxine Medication.
abstract: 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.
authors.affiliation: Division of Endocrinology & Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Hye In
authors.initials: HI
authors.lastname: Kim
authors.affiliation: Division of Endocrinology & Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Tae Hyuk
authors.initials: TH
authors.lastname: Kim
authors.affiliation: Division of Endocrinology & Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Hosu
authors.initials: H
authors.lastname: Kim
authors.affiliation: Division of Endocrinology & Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Young Nam
authors.initials: YN
authors.lastname: Kim
authors.affiliation: Department of Medical Education, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Hye Won
authors.initials: HW
authors.lastname: Jang
authors.affiliation: Division of Endocrinology & Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Jae Hoon
authors.initials: JH
authors.lastname: Chung
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Seong Mi
authors.initials: SM
authors.lastname: Moon
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Byung Woo
authors.initials: BW
authors.lastname: Jhun
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Hyun
authors.initials: H
authors.lastname: Lee
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Won-Jung
authors.initials: WJ
authors.lastname: Koh
authors.affiliation: Division of Endocrinology & Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
authors.forename: Sun Wook
authors.initials: SW
authors.lastname: Kim
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012189:Retrospective Studies; D012293:Rifampin / Q000494:pharmacology / Q000627:therapeutic use*; D012307:Risk Factors; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D013972:Thyrotropin; D013974:Thyroxine; D012293:Rifampin