Amiodarone Linked to Higher Risk of Thyrotoxicosis in AF Patients: Study
A new study published in the journal of Heart Rhythm showed that in individuals with atrial fibrillation, amiodarone therapy was independently linked to a higher incidence of thyrotoxicosis.
A common treatment for potentially fatal arrhythmias is amiodarone. Despite the fact that amiodarone has few adverse effects, 15-20% of patients may experience thyroid dysfunction. Amiodarone-induced thyrotoxicosis (AIT) is a serious side effect that can exacerbate heart failure and lead to arrhythmia recurrence.
While type II AIT is a destructive thyroiditis that reacts to glucocorticoids, type I AIT is often treated with thionamides and occurs in people who already have thyroid disease. There is a mixed kind that is linked to increased mortality, particularly in older persons with heart disease. For individuals who are intolerant or resistant to medical therapy, thyroidectomy is regarded as a last resort.
Research on the possibility of amiodarone-treated individuals developing thyrotoxicosis instead of hypothyroidism is yet lacking. Thus, this study evaluated the relationship between amiodarone and thyrotoxicosis in individuals who were diagnosed with hypothyroidism concurrently with atrial fibrillation (AF).
This research used the Clalit Health Services database to do a population-based retrospective cohort analysis. 2 distinct cohorts, 1 for hypothyroidism and the other for normal thyroid function, were identified from patients who received a new diagnosis of AF between 2010 and 2023. Amiodarone exposure was investigated as a time-dependent variable using Cox proportional hazard regression, which allowed participants to switch between exposure groups throughout follow-up.
The hypothyroidism cohort comprised 23,854 AF patients, of whom 107 (66 of 8,212 amiodarone users and 41 of 15,622 non-users) had thyrotoxicosis during follow-up.
This represents a crude incidence rate of 3.43 and 0.63 per 1000 person-years for amiodarone users and non-users, respectively. Amiodarone had an adjusted-HR of 5.18 (95% CI, 3.48-7.69) and was independently linked to an elevated incidence of thyrotoxicosis in this sample.
With an adjusted-HR of 15.02 (95% CI, 13.56-16.64) and an incidence rate of 19.78 and 1.14 per 1000 person-years for amiodarone users and non-users, respectively, the amiodarone impact was more pronounced in individuals with normal thyroid function. Overall, although amiodarone has a less impact on thyrotoxicosis risk in hypothyroidism patients, the risk is still high and should be used with caution.
Source:
Ryan, D., Gershinsky, R., Gronich, N., Yahav, A., Barnett-Griness, O., Schliamser, J. E., Saliba, W., & Danon, A. (2025). Association between amiodarone and thyrotoxicosis in patients with atrial fibrillation and hypothyroidism. Heart Rhythm: The Official Journal of the Heart Rhythm Society. https://doi.org/10.1016/j.hrthm.2025.08.003
