HealthDay News — Switching among generic levothyroxine products made by different manufacturers is not associated with clinically significant changes in serum thyrotropin (TSH) levels, according to a study published online February 28 in JAMA Internal Medicine.

Juan P. Brito, MD, from the Mayo Clinic in Rochester, Minnesota, and colleagues compared TSH levels among patients who continued taking the same sourced generic levothyroxine product and those who switched to a generic made by a different manufacturer. The analysis included 15,829 adults filling a generic levothyroxine prescription between January 1, 2008, and June 30, 2019.

The researchers found that 82.4% of adults continued taking the same sourced preparation, while 17.6% switched among generic levothyroxine preparations. Among 2780 propensity-matched patient pairs, the proportion of patients with a normal TSH level was similar between nonswitchers and switchers (82.7 and 84.5%, respectively). Similarly, the proportion of patients with a markedly abnormal TSH level after the index date was similar between the groups (3.1% among nonswitchers and 2.5% among switchers).

“These findings conflict with the current guideline recommendation that warns clinicians about potential changes in TSH level associated with switching among levothyroxine products sourced from different manufacturers,” the authors write.

One author disclosed financial ties to the pharmaceutical and medical devices industries.

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