From the FDA Drug Label
In studies in healthy subjects following single intravenous administration (5 mg/kg of amiodarone over 15 min), the plasma concentration vs time profile could be characterized by linear sum of four exponential terms with terminal elimination half-lives (t½) of 9 to 36 days for amiodarone and 9 to 30 days for DEA.
The half-life of amiodarone infusion for 24 hrs is not directly provided, but the terminal elimination half-lives (t½) of amiodarone range from 9 to 36 days after a single intravenous administration.
- The elimination half-life is not directly related to the infusion duration of 24 hours.
- The provided half-life range is for the terminal elimination phase, which occurs after the initial distribution phase.
- For a 24-hour infusion, the context is unclear, and the provided information does not directly answer the question regarding the half-life during this specific time frame 1.
From the Research
The half-life of amiodarone after a 24-hour infusion is approximately 55 days, as reported in the most recent and highest quality study 2. This extremely long half-life occurs because amiodarone is highly lipophilic and accumulates extensively in adipose tissue and highly perfused organs like the liver, lungs, and spleen. When administered intravenously for 24 hours, amiodarone initially distributes into tissues, followed by a very slow elimination phase. This prolonged half-life explains why amiodarone's effects persist long after discontinuation and why loading doses are typically required to achieve therapeutic levels quickly. Some key points to consider about amiodarone pharmacokinetics include:
- The drug undergoes hepatic metabolism primarily via CYP3A4 and CYP2C8 enzymes to its active metabolite, desethylamiodarone, which also has a long half-life 3.
- Due to this extended half-life, patients may experience continued antiarrhythmic effects for weeks to months after stopping the medication, and adverse effects may also persist for extended periods 4.
- Clinicians should be aware of this pharmacokinetic property when initiating, adjusting, or discontinuing amiodarone therapy, and consider the potential for drug interactions and toxicity 5, 6. The most important consideration in the use of amiodarone is its potential to cause significant toxicity, including effects on the thyroid, liver, and lungs, which necessitates careful monitoring and dose adjustment 4.