Rates of, and factors associated with, switching among generic levothyroxine preparations in commercially insured American adults.

IMPORTANCE: Some practice guidelines warn against generic L-thyroxine preparation switching. OBJECTIVE: To examine the rates of generic L-thyroxine preparation switching within one year of initiating L-thyroxine, and to examine factors associated with switching. DESIGN AND SETTING: Retrospective study using national data from a large administrative claims database from January 2008 through November 2018. PATIENTS: Medicare or commercially insured adults (≥18 years) who filled a generic L-thyroxine preparation. MAIN OUTCOME MEASURES: At least one switch from one generic L-thyroxine preparation to another within 1 year of L-thyroxine initiation defined by prescription fills. RESULTS: From January 2008 to November 2018, we included 483,390 patients who initiated generic L-thyroxine: mean (SD) age was 61.4 years (15.2), 75.2% were female, 72.6% were white. Within 1 year of initiating therapy, 98,013 (20%) switched to another L-thyroxine generic preparation at least once. In a multivariate logistic regression analysis, factors associated with switching included the number of pharmacies visited to fill L-thyroxine (>2 vs 1 adjusted OR [aOR] 7.15, 95% confidence interval [CI] 6.97-7.34), age ≥75 vs. <45 years (aOR 1.29, 95% CI 1.26-1.33), history of thyroid surgery (aOR 1.22, 95% CI 1.13-1.31), and first L-thyroxine fill date in 2018 vs. 2008 (aOR 3.32, 95% CI 3.14-3.51). CONCLUSIONS AND RELEVANCE: One in five patients switched among generic L-thyroxine manufacturers within one year of treatment initiation. Generic L-thyroxine switching occurred more often when more pharmacies were used to fill L-thyroxine. Given existing guideline recommendations, additional studies should clarify the impact of generic L-thyroxine switching on thyroid hormone values.

Cardiovascular outcomes and rates of fractures and falls among patients with brand-name versus generic L-thyroxine use.

PURPOSE: To compare cardiovascular outcomes and rates of fractures and falls among patients with persistent brand-name versus generic L-thyroxine use. METHODS: Retrospective, 1:1 propensity-matched longitudinal study using a national administrative claims database to examine adults (≥18 years) who initiated either brand or generic L-thyroxine between 2008 and 2018, censored at switch or discontinuation of L-thyroxine formulation or disenrollment from the health plan. Main outcome measures included rates of hospitalization for atrial fibrillation, myocardial infarction, congestive heart failure, stroke, spine and hip fractures, and rate of falls in the outpatient or inpatient setting. Hospitalizations for pneumonia were used as a negative control. RESULTS: 195,046 adults initiated treatment with L-thyroxine between 2008 and 2017: 87% generic and 13% brand formulations. They were mostly women (76%), young (94.6% under age 65), white (66%), and 47% had baseline thyroid stimulating hormone levels between 4.5 and 9.9 mIU/L. Among 35,667 propensity-matched patients, there were no significant differences between patients treated with brand versus generic L-thyroxine in atrial fibrillation (HR 0.96, 0.58-1.60), myocardial infarction (HR 0.66, 0.39-1.14), congestive heart failure (HR 1.30, 0.78-2.16), stroke (0.72, 0.49-1.06), spine (HR 0.87, 0.38-1.99) and hip fractures (HR 0.86, 0.26-2.82), or fall outcomes (HR 1.02, 0.14-7.32). Hospitalization rates for pneumonia (used as negative control) did not differ between groups (HR 0.85, 0.61-1.19). There were no interactions between brand versus generic L-thyroxine, these outcomes, and thyroid cancer, age, or L-thyroxine dose subgroups. CONCLUSIONS: We found no significant differences in cardiovascular outcomes and rates of falls and fractures for patients who filled brand versus generic L-thyroxine.