Amiodarone, thyroid hormone indexes, and altered thyroid function: long-term serial effects in patients with cardiac arrhythmias.
Amiodarone, a drug that has electrophysiologic actions resembling those of hypothyroidism, increases serum levels of T4 and reverse T3 (rT3) and decreases T3. The drug's long-term effects on thyroid function are poorly defined. Serial thyroid hormone indexes in 76 patients given amiodarone for 6 to 32 months (mean +/- standard deviation 16 +/- 7) for arrhythmias were determined serially. Over this period, 68 patients (89%) remained euthyroid; hypothyroidism developed in 6 (8%) and hyperthyroidism developed in 2 (3%). In patients who remained euthyroid, thyroid hormone alterations attained steady-state values at 3 months: T4 increased 42% (p less than 0.01), rT3 increased 172% (p less than 0.01) and T3 decreased 16% (p less than 0.05), without significant effect on thyroid stimulating hormone. For the euthyroid patients, the 90% tolerance limits (95% confidence) over the follow-up period for T4 was 5 to 19 micrograms/dl (normal 4 to 12), for T3 36 to 163 ng/dl (normal 60 to 160), for rT3 22 to 131 ng/dl (normal 15 to 50) and for thyroid stimulating hormone 0 to 14 microU/ml (normal 1 to 6). The changes in hormone indexes in hyperthyroid or hypothyroid patients were unrelated to the cumulative dose or duration of drug therapy. The most reliable diagnostic indexes for amiodarone-induced altered thyroid state were: thyroid stimulating hormone level over 20 microU for hypothyroidism and T4 over 20 ng/dl or high T3 over 200 ng/dl for hyperthyroidism. All levels were within the 90% tolerance limits derived for these hormones from patients remaining euthyroid on amiodarone long-term.(ABSTRACT TRUNCATED AT 250 WORDS)
D000638:Amiodarone / Q000009:adverse effects* / Q000627:therapeutic use; D001145:Arrhythmias, Cardiac / Q000188:drug therapy*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013959:Thyroid Diseases / Q000139:chemically induced*; D013960:Thyroid Function Tests; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood; D013997:Time Factors
D013963:Thyroid Hormones; D013972:Thyrotropin; D000638:Amiodarone