Jacksonville, FL—How does the use of generic versus brand-name therapy affect patients with predominantly benign thyroid disease and newly treated hypothyroidism?

A new study sought to answer that question in light of questions as to whether generic versions really are equivalent to brand-name levothyroxine.

The report, published ahead of print in Mayo Clinic Proceedings, focuses on whether generic and branded levothyroxine therapy affected hospitalization for cardiovascular events for patients at greater risk of coronary heart disease and heart failure.

Background information in the study points out that levothyroxine is the most prescribed medication in the United States, with more than 23 million prescriptions written annually.

The retrospective analysis used deidentified claims data from a large private U.S. health plan. Participants—80.2% were women aged 65 years and older—were followed for a mean of 1.0±1.2 years (range, 0-9.3 years).

Included in the analysis were 87,902 propensity score–matched patients—43,951 patients per cohort—initiating generic or brand L-T4. Defined as the primary outcomes were the event rates for hospitalizations for incident atrial fibrillation, myocardial infarction, congestive heart failure, or stroke.

Results indicated no differences in event rates (events per 1,000 person-years) for four 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).

Furthermore, stratification by age group revealed no differences, according to the researchers.

“In patients with newly treated hypothyroidism, cardiovascular event rates were similar for generic and brand L-T4,” study authors conclude.

“More than 90% of thyroid prescriptions are for levothyroxine, and there has been disagreement as to whether generic levothyroxine and branded thyroxine preparations are equivalent,” explained principal investigator Robert Smallridge, MD, a Mayo Clinic endocrinologist in Jacksonville. “These findings suggest that generic and brand levothyroxine therapy are similar as related to cardiovascular events risk.”

The authors call for confirmation with longer-term follow-up, as well as studies of subsets of patients, including those with a history of thyroid cancer, who frequently receive higher doses of levothyroxine.

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