Comparison of Incident Cardiovascular Event Rates Between Generic and Brand l-Thyroxine for the Treatment of Hypothyroidism.

Objective: To determine whether levothyroxine (L-T4) preparation (generic vs brand) affected hospitalization for cardiovascular events.

Patients And Methods: We performed a retrospective analysis using a large administrative claims database, OptumLabs Data Warehouse, creating two 1-to-1 propensity score-matched cohorts initiating generic or brand L-T4. Patients were followed for a mean of 1.0±1.2 years (range, 0-9.3 years). We included 87,902 propensity score-matched patients (43,951 patients per cohort) initiating generic or brand L-T4. Variables included in matching were age, sex, race/ethnicity, residence region, selected comorbidities, and Charlson-Deyo comorbidity score. Patients with previous use of any thyroid preparation, amiodarone, or lithium were excluded. Primary outcomes were the event rates for hospitalizations for incident atrial fibrillation, myocardial infarction, congestive heart failure, or stroke.

Results: In the generic L-T4 cohort, 35,242 (80.2%) were women and 7327 (16.7%) were 65 years of age or older; in the brand L-T4 cohort, 34,633 (78.8%) were women and 8092 (18.4%) were 65 years of age or older. We found no differences in event rates (events per 1000 person-years) for 4 outcomes comparing generic and brand L-T4 therapy: (1) atrial fibrillation (1.82 vs 2.19; hazard ratio [HR], 1.22; 95% CI, 0.90-1.65; P=.19); (2) myocardial infarction (2.12 vs 1.83; HR, 0.86; 95% CI, 0.64-1.17; P=.35); (3) congestive heart failure (2.27 vs 2.00; HR, 0.88; 95% CI, 0.66-1.18; P=.41); and (4) stroke (3.10 vs 2.38; HR, 0.77; 95% CI, 0.59-1.00; P=.05). Stratification by age group revealed no differences.

Conclusion: In patients with newly treated hypothyroidism, cardiovascular event rates were similar for generic and brand L-T4.