Amiodarone raises hypothyroidism in older atrial fibrillation patients

Amiodarone raises hypothyroidism in older atrial fibrillation patients


By Liam Davenport


16 October 2007


Am J Med 2007; 120: 880-885


MedWire News: Older males treated with amiodarone for persistent atrial fibrillation are substantially more likely to develop hypothyroidism than patients with atrial fibrillation who not given the treatment, US study findings indicate.


The majority of patients who are given amiodarone, which has recently been found to have unparalled effectiveness in maintaining sinus rhythm, are male, say Elizabeth Batcher, from West Los Angeles Veterans Affairs Medical Center in California, and colleagues. However, the long-term risk of amiodarone-induced thyroid dysfunction has not been thoroughly investigated.


The team therefore performed a substudy of 612 patients from the Sotalol Amiodarone Atrial Fibrillation Efficacy Trial, of whom 247 were treated with amiodarone and 365 were given sotalol or placebo. Sotalol and placebo patients were combined to form a control group, as neither would be expected to alter thyroid function, the authors note. The average age of the groups was 67.1 years for amiodarone-treated patients and 66.9 years among controls.


Thyroid function was measured at baseline, 3 month, 6 months, and every 6 months for up to 4.5 years by measuring serum thyroid-stimulating hormone (TSH) concentrations. There were no statistical differences in TSH levels at baseline between the groups.


The results indicate that subclinical hypothyroidism, defined as a TSH level of 4.5-10 mU/l, occurred in 25.8% of patients treated with amiodarone, compared with 6.6% of those from the control group, the team reports in the American Journal of Medicine.


In addition, 5.0% of amiodarone patients were found to have overt hypothyroidism, defined as a TSH level of over 10 mU/l, compared with just 0.3% of controls. In both cases, the difference between the amiodarone and control groups was significant.


Of the patients who developed TSH levels of more than 10 mU/l, 93.8% were detected by 6 months. It was also observed that amiodarone patients had a trend towards a greater prevalence of hyperthyroidism, defined as a TSH level of less than 0.35 mU/l, than controls, at 5.3% versus 2.4%.


The researchers write: "In summary, amiodarone-induced hypothyroidism developed in 30.8% of older men treated with amiodarone for chronic atrial fibrillation compared with the control group and presented early during therapy."


They add: "Given the high rate of hypothyroidism among patients taking amiodarone, monitoring of thyroid function is recommended at baseline, 3 months, and every 6 months thereafter during the therapy."


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