Thyroid

Switching from generic levothyroxine preparations does not affect thyroid hormone levels

Juan P. Brito, MD, MSc

February 28, 2022

2 minute read


Disclosures: Brito does not report any relevant financial information. Please see the study for relevant financial information from all other authors.


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According to the study data, adults who switch generic levothyroxine preparations from one manufacturer to another have no difference in average thyroid-stimulating hormone levels compared to those who do not switch.

According to guidelines published by the American Thyroid Association in 2014, providers are advised to avoid switching between generic levothyroxine products from different manufacturers. Juan P. Brito, MD, MScassociate professor of medicine and consultant in the division of endocrinology at the Mayo Clinic in Rochester, Minnesota, said the guidelines have led providers to prescribe brand name levothyroxine to most adults with hypothyroidism because doctors are unable to know when pharmacies change generics. some products.


Juan P. Brito, MD, MSc
Brito is a associate professor of medicine and consultant in the division of endocrinology at the Mayo Clinic in Rochester, Minnesota.

“We decided to do this study to test if switching between generic levothyroxine products had any effect on thyroid hormone values,” Brito told Healio. “In those who switch, we don’t see an impact on thyroid hormone levels compared to people who don’t switch. This sends a signal that switching is safe and keeping patients on generic levothyroxine n has no significant impact on thyroid hormone values.

Brito and colleagues conducted a retrospective study of anonymized administrative claims data from 2008 through June 2019 in the OptumLabs Data Warehouse, a database that includes enrollees in commercial insurance and Medicare Advantage programs across states. -United. The researchers included 15,829 adults who filled a prescription for generic levothyroxine from Mylan, Sandoz, or Lannett (mean age, 58.9 years; 73.4% female, 71.4% white). Adults with a stable prescription dose from the same manufacturer and a normal TSH level between 0.3 mIU/L and 4.4 mIU/L for at least 3 months were included in the analysis. TSH levels were collected from those who used the same generic prescription from a random refill date within one year of their first refill data, and from the switch date for adults who changed preparation.

The findings were published in JAMA internal medicine.

Of the study cohort, 82.4% continued to take the same generic preparation during the study period, and 17.6% switched at least once. The 2,780 adults who changed were matched with one adult from the unchanged group using propensity score matching. Among matched pairs, the percentage of adults with a normal TSH between 0.3 mIU/L and 4.4 mIU/L was similar between switchers (84.5%) and non-switchers (82.7%). Similarly, the proportion of adults with markedly abnormal TSH levels below 0.1 mIU/L or above 10 mIU/L was similar for switchers (2.5%) and non-switchers (3.1%). ). Mean TSH levels were 2.7 mIU/L in both groups.

In a subgroup of 364 adults receiving more than 100 g of levothyroxine per day, there was no significant difference between switchers and non-switchers in the percentage of those with normal TSH levels. There were also no associations observed in the sensitivity analysis.

Brito said the findings provide evidence for the ATA to update its recommendations to allow the switch to generic levothyroxine, noting that the switch can result in significant cost savings for patients currently taking brand name preparations.

“Levothyroxine is one of the most prescribed drugs in the United States,” Brito said. “It’s a huge market, and prescribing only brands is a significant expense for the healthcare system and for patients as well.

“Clinicians shouldn’t give patients a brand name just because they’re afraid to change,” Brito added. “They should revise the recommendation that we keep patients on the same product.”

For more information:

Juan P. Brito, MD, MSccan be reached at [email protected]