Amiodarone's most significant adverse effects include hepatitis, exacerbation of arrhythmias, worsening of congestive heart failure, thyroid dysfunction, and pulmonary fibrosis. Pulmonary fibrosis is frequently fatal and may not be reversed with discontinuation of the drug. Interestingly, despite significant prolongation of the QT interval, the risk of torsades de pointes is relatively low.
Patients with underlying sinus node dysfunction tend to have significant worsening of nodal function, frequently requiring pacemaker implantation. Corneal microdeposits develop in most adults receiving amiodarone. As many as 10% of patients complain of halos or blurred vision. The corneal microdeposits are reversible with stoppage of the drug.
Photosensitization occurs in 10% of patients. With continued treatment, the skin assumes a blue-gray coloration. The risk is increased in patients of fair complexion. The discoloration of the skin regresses slowly, if at all, after discontinuation of amiodarone.
3-7 hours after IV administration
Variable, weeks to months 2-10 days; 26-107 days with chronic administration Hepatic, active metabolites
Amiodarone inhibits the peripheral and possibly in-trapituitary conversion of thyroxine (T4) to triiodothyronine (T3) by inhibiting 5'-deiodination. The serum concentration of T4 is increased by a decrease in its clearance, and thyroid synthesis is increased by a reduced suppression of the pituitary thyrotropin T3. The concentration of T3 in the serum decreases, and reverse T3 appears in increased amounts. Despite these changes, most patients appear to be maintained in an euthyroid state. Manifestations of both hypothyroidism and hy-perthyroidism have been reported.
Tremors of the hands and sleep disturbances in the form of vivid dreams, nightmares, and insomnia have been reported in association with the use of amiodarone. Ataxia, staggering, and impaired walking have been noted. Peripheral sensory and motor neuropathy or severe proximal muscle weakness develops infrequently. Both neuropathic and myopathic changes are observed on biopsy. Neurological symptoms resolve or improve within several weeks of dosage reduction.
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