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Switching among generic thyroxine products is not responsible for serum thyrotropin changes
Clinical Question
Does switching among generic levothyroxine products change serum thyrotropin levels?
Bottom line
Missed doses, drug interactions, or even food interference can affect levothyroxine and, therefore, TSH results. This study points out that changes in sources of generic levothyroxine, however, do not. When TSH results drop out of the normal range, ask patients whether and with what they are taking their daily dose and not whether their pharmacy has changed the manufacturer of their prescription. 2b
Reference
Study design: Cross-sectional
Funding: Government
Setting: Outpatient (any)
Synopsis
These researchers used insurance data for 15,839 patients who received generic levothyroxine at a stable dose and had a normal serum thyrotropin (TSH) level for at least 3 months. Although most patients continued to receive levothyroxine from the same drug manufacturer, 2780 (17.6%) switched among generic levothyroxine preparations. The researchers matched these patients with similar nonswitching patients. Among these pairs, the proportion of patients with normal TSH levels measured 6 weeks to 12 months was similar between the 2 groups: 82.7% among the nonswitching patients and 84.5% among the switching patients. Similarly, 3.1% of nonswitching patients and 2.5% of switching patients had markedly abnormal levels of TSH (< 0.1 mIU/L or > 10 mIU/L).
Reviewer
Allen F. Shaughnessy, PharmD, MMedEd
Professor of Family Medicine
Tufts University
Boston, MA
Comments
Levothyroxine introduced in patients with routine management
Levothyroxine does not in any way affect the pituitary axis thereby letting us understand the efficacy is equivalent to thyroxin
changing thyroxin products
this does not change TSH levels