100 QUESTIONS IN CARDIOLOGY

85 What percentage of patients will suffer the

complications of amiodarone therapy, and how

reversible are the eye, lung, and liver changes?

How do I assess thyroid function in someone on

amiodarone therapy?

Daniel E Hillman

Amiodarone therapy is associated with a number of serious

toxicities which primarily involve the lung, heart, liver or thyroid

gland. The drug is also associated with a wide array of other side

effects involving the skin, eye, gastrointestinal tract and

neurologic system. Drug discontinuance rates with amiodarone

are closely related to its daily dose. The table summarises the

cumulative incidence of adverse reactions reported in two

separate meta-analyses.1,2

Eye, lung, and liver toxicity are all potentially reversible if

amiodarone is discontinued early after the development of

toxicity. However, cases of permanent blindness, death from liver

failure and death from respiratory failure have been rarely

reported with amiodarone.

There are no adequate predictors of pulmonary toxicity, and

serial lung function studies are usually not helpful. Dose and

duration of treatment are no guide to risk. Clinical suspicion must

remain high, especially in the elderly or those with co-existent

pulmonary disease.^3

Amiodarone has been implicated as a cause of both hyper-

thyroidism and hypothyroidism. Hypothyroidism is a predictable

response to the iodide load presented by amiodarone. Two types

of hyperthyroidism have been reported to occur with

amiodarone. Type I amiodarone-induced hyperthyroidism occurs

in patients with underlying thyroid disease such as Graves

disease. The iodide load in these patients accelerates thyroid

hormone synthesis. Type II amiodarone-induced hyperthyroidism

occurs in patients with normal thyroids. Hyperthyroidism results

from a direct toxic effect of amiodarone causing a subacute

destructive thyroiditis with release of preformed thyroid

hormone. Patients receiving amiodarone should have thyroid

function evaluated at periodic intervals. A low TSH is indicative of

hyperthyroidism, but does not distinguish between Type 1 and

Type 2 hyperthyroidism. Radioactive iodine uptake may be low