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The Association Between Switching from Synthroid® and Clinical Outcomes: US Evidence from a Retrospective Database
James V Hennessey1, Ramon Espaillat2, Yinghui Duan2
1Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA, 02215, USA.
Advances in Therapy
|October 28, 2020
Summary
Switching levothyroxine formulations increases the risk of out-of-range thyroid-stimulating hormone (TSH) levels and adverse clinical outcomes. Continuous Synthroid® use is associated with better TSH control and fewer negative health events.
Area of Science:
- Endocrinology
- Pharmacology
- Public Health
Background:
- Clinical guidelines advocate consistent levothyroxine therapy for hypothyroidism.
- Switching between synthetic levothyroxine formulations is discouraged.
Purpose of the Study:
- To compare clinical outcomes between continuous Synthroid® users and patients switching to alternative levothyroxine formulations.
- To assess the likelihood of adverse clinical outcomes associated with levothyroxine formulation switching.
Main Methods:
- Retrospective cohort analysis of electronic health records (May 2000-March 2016).
- Propensity score matching created cohorts of continuous Synthroid® users and switchers.
- Outcomes included out-of-range TSH levels and a composite endpoint of adverse clinical conditions.
Main Results:
- Switchers were more likely to have out-of-range TSH levels (OR 1.15; 95% CI 1.08-1.23).
- Switchers had a higher likelihood of the composite clinical endpoint (OR 1.23; 95% CI 1.12-1.37).
- Specific adverse outcomes like chronic kidney disease, depression, fatigue, and hypertension were more prevalent in switchers.
Conclusions:
- Findings support guidelines recommending against switching levothyroxine formulations.
- Continuous Synthroid® use is linked to better TSH control and reduced adverse clinical outcomes.
- Avoiding formulation switches is crucial for managing hypothyroidism effectively.
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