Amiodarone is a Class III antiarrhythmic with a complex pharmacokinetic profile. Which of the following statements about amiodarone pharmacokinetics is CORRECT?
- A Amiodarone is primarily renally excreted unchanged and dose must be halved in renal failure
- B Volume of distribution is extremely large (~60 L/kg), necessitating loading doses; elimination half-life is 40–55 days ✓
- C Oral bioavailability approaches 100% due to no first-pass metabolism
- D Plasma half-life is 6–12 hours, similar to other class III agents
Correct answer: B. Volume of distribution is extremely large (~60 L/kg), necessitating loading doses; elimination half-life is 40–55 days
Explanation
Amiodarone is extremely lipophilic and accumulates extensively in adipose, liver, lung, and skin, giving a massive volume of distribution (approximately 60 L/kg). Loading doses are required to achieve tissue saturation. Its plasma elimination half-life is 40–55 days (up to 100 days reported), meaning that adverse effects (pulmonary toxicity, thyroid dysfunction, corneal deposits) may persist for months after discontinuation. Oral bioavailability is variable (35–65%) and it undergoes hepatic CYP3A4 metabolism to the active metabolite desethylamiodarone.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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