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No difference in thyroid dysfunction when using brand-name, generic drugs
Kesselheim AS. CMAJ. 2011;doi:10.1503/cmaj.110808.
Tsadok MA. CMAJ. 2011;doi:10.1503/cmaj.101800.
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New data indicate that the incidence of thyroid dysfunction does not differ whether patients use a generic formulation of amiodarone or a brand-name version of the drug.
Previous research has linked the antiarrhythmic agent to an elevated risk for thyrotoxicosis and hypothyroidism, raising concern that this risk may increase when generic formulations of the drug are prescribed in place of the brand-name version. To investigate this concern, researchers in Canada conducted a retrospective cohort study comparing the incidence of thyroid dysfunction among patients using generics with those using the brand-name version of the drug (Cordarone, Wyeth-Ayerst Laboratories; Pacerone, Upsher-Smith Laboratories).
The researchers identified 60,220 patients aged at least 66 years with atrial fibrillation who met inclusion criteria. Of these patients, 4.7% were prescribed the brand-name version of amiodarone, whereas 10.4% were prescribed a generic formulation at the beginning of the study period. Median maintenance dose of amiodarone between both groups was 200 mg daily.
Incidence of thyroid dysfunction was 14.1 per 100 person-years for both groups, with 16.8% of patients using the brand-name version and 17.9% using a generic formulation experiencing problems after a mean follow-up of 1.2 years and 1.3 years, respectively. A multivariate analysis also revealed no significant difference in incidence rates of thyroid dysfunction between the two cohorts (HR=0.97; 95% CI, 0.87-1.08). Results indicated that hypothyroidism was the most common problem, and rates of hyperthyroidism were comparable between groups. The mean time to onset of thyroid dysfunction was also similar between patients using the brand-name drug (4.32 years) and those using a generic (4.09 years). The researchers, however, identified female sex, increasing age and chronic obstructive pulmonary disease as factors associated with increased risk for thyroid dysfunction.
Data also showed that a larger proportion of patients using the brand-name formulation (54.6%) discontinued use compared with patients taking the generic version (43.8%). Furthermore, 44.6% of patients taking the brand-name drug switched to a generic, whereas only 4% who were initially prescribed a generic switched to the brand-name formulation.
“We found no difference in the incidence of thyroid dysfunction between generic and brand-name formulations,” the researchers wrote. “The results from this study provide valuable information for both clinicians and policymakers concerning the prescription of brand-name vs. generic drugs.”
In an accompanying commentary, Aaron S. Kesselheim, MD, JD, of Brigham Women’s Hospital in Boston, said these results support the safety of generic drugs, although caution is warranted.
“Decades of experience and numerous clinical studies suggest that patients and physicians can be confident in the bioequivalence of brand name and generic drugs approved by Health Canada, the FDA or other similar regulatory authorities,” Kesselheim wrote. “In rare circumstances where there is concern over interchangeability, such as for high-risk patients, it may be reasonable for physicians to take extra precautions, such as additional monitoring, when substitution occurs.”
Disclosure: Some researchers report receiving grants, consulting and speaker fees from Boehringer Ingelheim, Medtronic and Sanofi-Aventis. Dr. Kesselheim reports no relevant financial disclosures.
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