From the Guidelines
Amiodarone loading for acute arrhythmias typically involves 150 mg IV over 10 minutes, followed by 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours, as recommended by the most recent guidelines 1.
Key Considerations
- The dosage of amiodarone should be kept at the lowest effective level to minimize potential drug toxicity and interactions 1.
- For oral loading, 400-800 mg daily divided into 2-3 doses is used for 1-2 weeks, followed by maintenance of 200-400 mg daily 1.
- Side effects include hypotension, bradycardia, QT prolongation, and phlebitis with IV administration 1.
- Long-term use requires monitoring for pulmonary, thyroid, liver, and ocular toxicity 1.
Mechanism of Action
- Amiodarone works by blocking potassium channels, prolonging action potential duration, and exhibiting class I, II, III, and IV antiarrhythmic properties 1.
- It has a very long half-life (15-142 days) due to extensive tissue distribution and slow elimination, which explains why loading doses are necessary to achieve therapeutic effects quickly 1.
Important Interactions
- Amiodarone is a substrate of and inhibits P-glycoprotein and CYP2C9, CYP2D6, and CYP3A4, and is an inhibitor of OCT2 1.
- Reduce warfarin dose by 50%, and reduce digoxin dose by 30%–50% when co-administered with amiodarone 1.
From the Research
Amiodarone Loading Dose
- The loading dose of amiodarone can be administered intravenously or orally, with the goal of achieving a therapeutic serum concentration quickly 2, 3.
- A study published in 1984 found that an intravenous amiodarone infusion designed to achieve and maintain a serum concentration of 2 to 3 micrograms/ml was effective in rapidly suppressing complex ventricular arrhythmias 2.
- Oral loading doses of amiodarone have also been studied, with one study using a dose of 50 mg/kg per day for 3 days, followed by 30 mg/kg per day for 2 days, and then a maintenance dose of 300 to 400 mg twice daily 3.
- Another study used a high-dose oral loading regimen of 1,200 to 1,400 mg/day to treat frequent, refractory, sustained ventricular arrhythmias, with arrhythmias controlled in 10 patients within 6 days 4.
Efficacy and Safety
- Amiodarone has been shown to be effective in suppressing ventricular arrhythmias, with one study finding an 85% reduction in episodes of ventricular tachycardia 2.
- However, amiodarone can also have significant side effects, including gastrointestinal, cardiovascular, and neurologic effects, as well as thyroid dysfunction and pulmonary toxicity 5, 6.
- High-dose oral loading regimens have been found to be safe and effective in controlling ventricular arrhythmias, but caution should be exercised when using large intravenous doses in patients with severely impaired left ventricular function 2, 4.
Clinical Use
- Amiodarone is an effective antiarrhythmic medication that is frequently used in practice for both ventricular and atrial arrhythmias 6.
- Clinicians should be aware of the indications, contraindications, dosing, side effects, and interactions of amiodarone to ensure safe and effective use 6.
- Routine monitoring is recommended to detect potential side effects, such as thyroid abnormalities, pulmonary fibrosis, and transaminitis 6.