Levothyroxine

Loren Bonner

Despite continued debate, practice guidelines state that adult patients with hypothyroidism should consistently use the same levothyroxine product. But a new study published in JAMA Internal Medicine could make the case for a revision.

Researchers from the Mayo Clinic, FDA, and the Yale School of Medicine found that switching one generic levothyroxine product with another does not have a significant effect on a patient’s thyroid-stimulating hormone (TSH) levels. In the large retrospective comparative effectiveness study, which included 15,829 patients, researchers found a nonsignificant difference between patients who used the same levothyroxine product and those who switched between generic products: 83% of patients who filled a generic levothyroxine prescription and used the same product had normal TSH levels versus 85% of patients who switched between generic products.

Results of the study suggest that switching among different generic levothyroxine products was not associated with clinically significant changes in TSH levels.

“Among those people who switched, we didn’t see an impact on thyroid hormone levels, which I think sends a signal that switching is actually safe,” said Juan Brito, MD, lead author of the study.

Betty Dong, PharmD, FASHP, FAPhA, FCCP, said the study should make prescribers as well as the American Thyroid Association (ATA)—the association that publishes levothyroxine guidelines—more comfortable about using generic levothyroxine preparations.

“These cost-effective levothyroxine preparations should be prescribed more often,” said Dong, a professor of clinical pharmacy and family and community medicine at the University of California Schools of Pharmacy and Medicine in San Francisco. “Pharmacists can feel more comfortable recommending these generic levothyroxine preparations for formularies.”

She said pharmacists should provide more education about suitability and efficacy of generic levothyroxine preparations to laypersons, prescribers, and formulary systems.

“All pharmacists should be aware of the data from this article,” said Dong. “Pharmacists should use generic terminology when discussing levothyroxine preparations.”

An age-old debate

Levothyroxine is one of the most widely prescribed medications in the United States. But brand-name levothyroxine is significantly more expensive for patients as well as to the health care system overall, said Brito.

To give an idea of how much patients can save, Brito, who is from the Mayo Clinic in Rochester, MN, notes that a 90-day supply of brand levothyroxine is about $130 but a 90-day supply of generic levothyroxine is about $10.

Current guidelines state that patients should stay on the same product—whether brand or generic—because of the concern of different concentrations of thyroid hormone in another medication affecting thyroid values.

“The problem with that recommendation is that the recommendation indirectly supports the use of brand,” said Brito.

This is because pharmacists can switch patients to generic products at any point and providers are avoiding that by writing patients prescriptions for brand levothyroxine only.

“In order to keep up with the guidelines and maintain the recommendation in practice, the easiest way to maintain the same level levothyroxine product is to keep the patients on brand,” said Brito.

“We know endocrinologists prefer brand therapy and brand therapy continues to be used significantly more for thyroid [hormone] replacement as opposed to other conditions in which you have both generic and brand,” Brito said.

Updating guidelines

Findings from this study conflict with the current guideline recommendation that warns clinicians about potential changes in TSH levels associated with switching among levothyroxine products sourced from different manufacturers.

“Updated revisions to the ATA’s recommendations on treatment of hypothyroidism should incorporate these recent findings,” said Dong.

The authors did not study brand versus generic preparations interchangeability, and Dong said she hopes this research group will perform a similar comparison looking at brand versus generic levothyroxine. ■