NEW YORK (Reuters) – Switching among generic levothyroxine sodium products made by different manufacturers does not result in clinically significant changes in serum thyrotropin (TSH) levels, according to a comparative-effectiveness study.
The finding challenges current American Thyroid Association guidance that recommends avoiding switches between levothyroxine products sourced from different manufacturers.
To maintain the same levothyroxine product, the guideline recommends that clinicians prescribe either the same identifiable product of generic levothyroxine (sourced from the same manufacturer) or a specific brand of levothyroxine.
“This recommendation indirectly fueled brand-name levothyroxine use over generic, particularly among endocrinologists,” Juan Brito, MBBS, of Mayo Clinic in Rochester, Minn., told Reuters Health by email.
“Furthermore, higher use of generic will represent a significant saving for patients and the health care system,” Dr. Brito noted.
This recommendation is also at odds with the Food and Drug Administration stance that approved generic levothyroxine products are expected to be interchangeable with no need for serum TSH testing.
For their study, Dr. Brito and colleagues compared TSH levels among 13,049 patients who continued taking a generic levothyroxine product from the same source and 2,780 patients who switched among generic levothyroxine preparations. They used propensity-score matching to minimize confounding.
The proportion of patients with a normal TSH level (after an index date) was not significantly different among patients who continued to use the same product and among those who switched between generic products (82.7% vs. 84.5%).
“Switching among generic levothyroxine products sourced from different manufacturers was not associated with differences in achieving a normal TSH level or with changes in TSH levels compared with continuing to take the same sourced levothyroxine,” Dr. Brito and colleaguesin JAMA Internal Medicine.
“These results may reassure patients and clinicians that switching among generic levothyroxine products is unlikely to have substantial implications for treatment effects,” they said.
Dr. Brito told Reuters Health he’s not surprised by the findings.
“In practice, I have not seen a clinical signal that keeping patients on generic levothyroxine affected their thyroid values compared to patients using only the same brand,” Dr. Brito noted.
“Also, we knew that previous evidence suggesting that switching affected thyroid hormone values was not great, and it was mostly coming from studies funded by brand name manufacturers,” he added.
The study was supported by grants from the FDA and the U.S. Department of Health and Human Services. The authors have no relevant disclosures.
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