Amiodarone‐induced Hyperthyroidism: Assessment of the Predictive Value of Biochemical Testing and Response to Combined Therapy Using Propylthiouracil and Potassium Perchlorate*

Abstract

In order to assess the value of thyroid function testing during amiodarone therapy, we reviewed all available tests in 128 patients treated with this drug. Nine patients (7.0%) developed biochemical hyperthyroidism with elevation of both free thyroxine index (FT4I) and free triiodothyronine index (FT3I) and marked suppression of serum thyroid stimulating hormone (TSH) after 1-46 months of therapy; six of these nine patients had clear clinical evidence of thyroid overactivity. Where serial tests were available before development of hyperthyroidism, this complication developed suddenly, despite previously stable normal indices of thyroid function, and could not be predicted by currently-available biochemical tests such as T4, T3, sensitive TSH, thyroglobulin or sex hormone binding globulin (SHBG) assays. Clinical features such as unexplained weight loss, proximal myopathy, exacerbation of arrhythmia, or heat intolerance appear to be the key to prompt diagnosis of this complication. Hyperthyroxinemia without T3 excess was found in 32.8% of patients without progression to true hyperthyroidism. Serum TSH remained detectable by sensitive assay in 17 out of 18 patients with amiodarone-induced euthyroid hyperthyroxinemia and was significantly higher than in patients with equivalent hyperthyroxinemia due to thyroxine therapy. Serial levels of SHBG were higher in patients with true hyperthyroidism than in those with euthyroid hyperthyroxinemia. The effect of combined treatment with propylthiouracil (800 mg/day) and potassium perchlorate (800 mg/day) was evaluated in five of the six clinically hyperthyroid patients. Biochemical euthyroidism was achieved after 7-19 weeks, a response slower than previously reported, indicating that this drug combination does not result uniformly in prompt resolution of amiodarone-induced hyperthyroidism.

Amiodaron i tarczyca

“…czynność tarczycy indukowana AMIO zwykle wystę-puje po kilku miesiącach leczenia AMIO, ale może też wystąpić w ciągu kilku początkowych tygodni leczenia [32]. Początek AIT zależy od typu AIT, krótszy jest w przypadku typu 1 niż w typie 2 (patrz poniżej) [33].…”

“…AIT usually develops after months of AMIO treatment, but it can develop in the first few weeks of therapy [32]. The onset time of AIT depends on AIT type, being shorter in type 1 than in type 2 AIT (see below) [33].…”

Disfunción tiroidea inducida por amiodarona en la práctica clínica

“…Perclorato de potasio (KClO4) ha sido asociado con anemia aplásica, pero ningún caso ha sido informado cuando se ha usado para tratar TIA 1. En los pacientes que reciben grandes dosis de DAT más KClO4, parece razonable recomendar el monitoreo bisemanal del recuento leucocitario (27,28) .…”

Benzofuran derivatives and the thyroid

“…Studies have shown that discontinuation of perchlorate from the combination therapy after about 6 weeks for patients on amiodarone therapy can achieve euthyroidism within 2 -5 weeks. 66,72 Perchlorate has serious adverse effects including agranulocytosis and aplastic anaemia as well as renal impairment at doses exceeding 1 g daily. 44 It is relatively safe at lower doses and that the dosage is tapered or stopped after about Lithium is concentrated by the thyroid and inhibits thyroidal iodine uptake.…”

“…65 SHBG levels may also be increased in AIT patients. 66 Subclinical hyperthyroidism may occur in those without symptoms whose serum TSH levels are suppressed with T 3 remaining within the reference range. Distinguishing the two AIT subtypes may be difficult on clinical grounds but clinical indicators may help differentiate.…”