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Possible Effects of Amiodarone

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Question

A 64-year-old woman treating “arrythmia” with metoprolol 100mg bd (p.o.) has presented symptomatic ventricular extrasystoles and was treated with amiodarone acutely in the ER and released to continue metoprolol. In the ambulatory the cardiologist prescribed amiodarone but she used it for about 10 days only. In the mean time she had got these lab values: TSH 2,67, FT4 3,10 and was led to the endocrinologist.She had no clinical evidence of arrythmia. There were no signs or symptoms tha t could be atributed to thyrotoxicosis. She lost 9kg over about 6 months, 5kg of then over the last 3 months, then stabilized, but it could be atributed to fluoxetine that she started in that period. Her sister had nodular goiter and was subjected to hemithyroidectomy and uses levothyroxine; she has normal TSH under therapy but FT4 was not available.

Further results six weeks later were: TSH 3,55, FT4 2,33. Ultra-soud: normal thyroid, volume 13cc, 4 small colloid cysts. Antibodies negative.

I thought it could be either Resistance to Thyroid hormone (RTH) or TSH-oma and asked for TRH stimulation test four weeks later, but I was surprised that FT4 was normal e T3 was low: TSH 3,12 – TRH Stimulus: 15′ – 3,22; 30′ – 14,40 (4,6x). FT4 1,50. Total T3 0,67 (normal 0,87-1,78). Alfa subunit – 945 (basal) – 30′ after TRH stimulus: 1070 (1,13X) – reference for basal: 340-4000. SHBG 18,5 (reference 18-114) – low value can be atributed to menopause. It could be effect of inhibition of deiodinase by amiodarone but its use was short; or by beta-blocker but as long as I know it happens with propranolol and not with other beta-blockers.What is your opinion?

Marcello Molima, Brazil

Response

Amiodarone has a long half-life in the body. The patient has been exposed to two drugs that inhibit T4>T3 conversion. Her TSH remains normal, and she has no signs of hyperthyroidism. T3 is now low. Thus everything points to a drug effect that may dissipate over some weeks or months. I believe it would be best to wait to see how the situation progresses.

Best regards,

L De Groot, MD.