NEW YORK (Reuters Health) – Among patients with atrial fibrillation on amiodarone, the incidence of thyroid dysfunction is identical in those taking the brand-name formulation of the drug and those taking a generic version, according to the results of a Canadian study.
Dr. Louise Pilote, at McGill University Health Center in Montreal, Quebec, and colleagues found that thyroid dysfunction occurs in about 17% of AF patients on amiodarone. Writing in the Canadian Medical Association Journal, they advise: “Given that thyroid dysfunction affects almost one in five patients taking amiodarone, patients with atrial fibrillation should be made aware of this risk when they start treatment with amiodarone to ensure that any symptoms are recognized and reported to their clinicians as early as possible for monitoring, timely follow-up and possible treatment.”
Prompted by concerns about the potential for adverse effects with generic formulations of amiodarone, the researchers conducted a retrospective study of more than 60,000 patients with atrial fibrillation. Within this cohort, 2804 (4.7%) were taking the brand-name formulation of amiodarone and 6278 (10.4%) the generic formulation.
Thyroid dysfunction — most often hypothyroidism but sometimes hyperthyroidism, and occasionally both in some patients — occurred in 16.8% of those taking brand-name amiodarone and 17.9% of those taking generic amiodarone. In terms of incidence, this translated to a rate of thyroid dysfunction of 14.1 per 100 person-years in both groups, according to the report.
The mean time to clinically apparent thyroid dysfunction after starting amiodarone was 4.32 years with the brand-name drug and 4.09 years with the generic version, the team found. Female gender, increasing age, and COPD were associated with increased risk of thyroid dysfunction.
They authors suggest that their findings “provide valuable information for both clinicians and policy-makers concerning the prescription of brand-name versus generic drugs.”
Related to that point, Dr. Aaron Kesselheim of Brigham and Women’s Hospital in Boston states in a commentary: “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.”
Amiodarone-induced thyroid dysfunction: brand-name versus generic formulations