Study: Here’s Some Evidence That Switching Among Generic Levothyroxine Products Is OK

Guidelines tell prescribers and patients to avoid switching among levothyroxine products from different manufacturers. But Mayo Clinc-led research finds little difference between switchers and nonswitchers.

Even prescribers who are completely comfortable with writing scripts for generics or biosimilars may have some reservations about switching patients who are stable on a brand-name drug to generic or switching from one generic to another.

A study published today in JAMA Internal Medicine is evidence that those reservations may be misplaced, at least with respect to generic levothyroxine sodium.

Synthroid is the well-known brand-name version of levothyroxine.

Levothyroxine is one of the most commonly prescribed drugs in the U.S. It is used to treat low thyroid hormone levels (hypothyroidism), which can be consequence of an enlarged thyroid gland, an injured thyroid gland, or thyroid cancer.

A team of researchers led by Juan P. Brito, M.D.,M.Sc., an endocrinologist at the Mayo Clinic, compared 2,780 adult patients who switched among levothyroxine preparations to a control group of “nonswitchers” who stayed with the particular levothyroxine generic they were prescribed.

They found little difference in the proportion of patients with normal thyroid stimulating hormone (TSH) in the switcher and the nonswitcher groups (84.5% vs. 82.7%). Likewise, there was little difference in the proportion of patients with abnormal TSH levels: 2.5% among the switchers compared with 3.1% among the nonswitchers.

The study was designed so the switchers and nonswitchers were comparable.

Brito and his colleagues noted that the American Thyroid Association guidelines recommend against switching among levothyroxine products from different manufacturers. “Given that generic levothyroxine products can be switched at the pharmacy level without notifying or requiring approval from clinicians or patients, this recommendation may have indirectly fueled the preferential use of brand-name levothyroxine, particularly among endocrinologists,” they wrote in the discussion section of their paper. They note that 40% of the prescriptions for levothyroxine written by endocrinologists were for brand-name levothyroxine compared with just 15% of the prescriptions written by primary care practitioners.