The authors administered to 13 patients with auricular fibrillation amiodarone (Cordarone), 1200 mg/day, by the oral route from the 4th to the 10th day of the trial, 600 mg per day from the 11th to the 13th day of the trial. Simultaneously the patients were given digoxin, 1 mg, by the i.v. route: on the first day 1 mg i.v., 2nd to 5th day 0.5 mg i.v., and on the 6th to 10th day of the trial 0.25 mg. They assessed the serum digoxin concentration on the 1st, 4th, 11th and 14th day, the serum concentration of triiodothyronine (T3), thyroxine (T4) and thyrotropic hormone (TSH) on the 1st and 14th day of the trial. The authors revealed that after ten days administration of amiodarone T4 does not change (102.4 +/- 28.2 nmol/l vs. 101.3 +/- 13.4 nmol/l, NS), T3 declines significantly (2.47 +/- 0.85 nmol/l vs. 1.86 +/- 0.54 nmol/l, p less than 0.001) and TSH rises insignificantly (2.82 +/- 1.18 mU/l vs. 3.34 +/- 1.43, NS). Consistent with data in the literature on the effect of several weeks administration of amiodarone on thyroid function, the authors assume inhibition of 5'monodeiodization of T4 with a reduced formation of T3 and increased formation of rT3. The drop of T3 may play a part also in the antiarrhythmic action of amiodarone in the treatment of auricular fibrillation.

Keywords: Aged; Amiodarone /pharmacology/; Digoxin /pharmacology/; Female; Humans; Male; Thyroid Gland /drug effects/; Thyroid Hormones /metabolism/