Prevalence and factors associated with chronic use of levothyroxine: A cohort study

PLoS One. 2021 Dec 20;16(12):e0261160. doi: 10.1371/journal.pone.0261160. eCollection 2021.

Abstract

Importance: Levothyroxine prescriptions are rising worldwide. However, there are few data on factors associated with chronic use.

Objective: To assess the prevalence of chronic levothyroxine use, its rank among other chronic drugs and factors associated with chronic use. To assess the proportion of users outside the therapeutic range of thyroid-stimulating hormone (TSH).

Design: Cohort study (CoLaus|PsyCoLaus) with recruitment from 2003 to 2006. Follow-ups occurred 5 and 10 years after baseline.

Participants: A random sample of Lausanne (Switzerland) inhabitants aged 35-75 years.

Main outcomes: We evaluated the prevalence of chronic levothyroxine use and we then ranked it among the other most used chronic drugs. The ranking was compared to data from health insurance across the country. We assessed the association between each factor and chronic levothyroxine use in multivariable logistic regression models. The proportion of chronic levothyroxine users outside the usual TSH therapeutic range was assessed.

Results: 4,334 participants were included in the analysis (mean±SD age 62.8±10.4 years, 54.9% women). 166 (3.8%) participants were chronic levothyroxine users. Levothyroxine was the second most prescribed chronic drug after aspirin in the cohort (8.2%) and the third most prescribed when using Swiss-wide insurance data. In multivariable analysis, chronic levothyroxine use was associated with increasing age [odds ratio 1.03, 95% confidence interval 1.01-1.05 per 1-year increase]; female sex [11.87 (5.24-26.89)]; BMI [1.06 (1.02-1.09) per 1-kg/m2 increase]; number of concomitant drugs [1.22 (1.16-1.29) per 1-drug increase]; and family history of thyroid pathologies [2.18 (1.37-3.48)]. Among chronic levothyroxine users with thyroid hormones assessment (n = 157), 42 (27%) were outside the TSH therapeutic range (17% overtreated and 10% undertreated).

Conclusions: In this population-based study, levothyroxine ranked second among chronic drugs. Age, female sex, BMI, number of drugs and family history of thyroid pathologies were associated with chronic levothyroxine use. More than one in four chronic users were over- or undertreated.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Cohort Studies
  • Diabetes Mellitus / drug therapy*
  • Diabetes Mellitus / pathology
  • Drug Utilization / statistics & numerical data*
  • Female
  • Humans
  • Hypertension / drug therapy*
  • Hypertension / pathology
  • Male
  • Middle Aged
  • Thyroid Gland / drug effects
  • Thyroid Gland / pathology*
  • Thyroxine / therapeutic use*

Substances

  • Thyroxine

Grants and funding

The work of CJP and LW is partly funded by a grant from the Swiss National Science foundation (SNSF 320030-172676 to NR). The CoLaus|PsyCoLaus study was and is supported by research grants from the Swiss National Science Foundation (grants 3200B0–105993, 3200B0-118308, 33CSCO-122661, 33CS30-139468, 33CS30-148401 and 32473B-182210) and the SNSF 32003B-173092 to GW, GlaxoSmithKline, and the Faculty of Biology and Medicine of Lausanne. This research was supported by SASIS AG and santésuisse. They provided support in the form of salaries for authors OG and PW, but did not have any additional role in the study design, data collection and analysis, decision to publish or preparation of the manuscript. The specific roles of these authors are articulated in the “author contributions” section.