Amiodarone has a uniquely long half-life of approximately 40–55 days. The primary pharmacokinetic reason for this is:

• A Extensive renal tubular reabsorption preventing urinary elimination
• B Formation of an active metabolite (desethylamiodarone) with a longer half-life than the parent
• C High plasma protein binding preventing hepatic extraction and metabolism
• D Extremely large volume of distribution (~60 L/kg) due to accumulation in adipose tissue and organs ✓

Explanation

Amiodarone is highly lipophilic and has an enormous volume of distribution (~60 L/kg), meaning it distributes extensively into fat, liver, lung, and other tissues. This massive tissue binding creates a large reservoir from which drug slowly returns to plasma for elimination. The result is a terminal half-life of 40–55 days after long-term therapy. This prolonged half-life has important clinical implications: drug effects persist weeks after discontinuation and loading doses are required at initiation.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.