What is the recommended dosing when switching from intravenous (IV) amiodarone to oral (PO) amiodarone?

Switching from IV to PO Amiodarone

When switching from IV amiodarone to oral amiodarone, the recommended dosing depends on the duration of IV therapy: patients who received IV amiodarone for less than one week should take 800-1,600 mg oral amiodarone per day; those who received IV amiodarone for 1-3 weeks should take 600-800 mg oral amiodarone per day; and those who received IV amiodarone for more than 3 weeks should take 400 mg oral amiodarone per day. 1

Conversion Protocol Based on Duration of IV Therapy

The conversion from IV to oral amiodarone should follow these specific guidelines:

• Less than 1 week of IV therapy: 800-1,600 mg PO daily in divided doses
• 1-3 weeks of IV therapy: 600-800 mg PO daily in divided doses
• More than 3 weeks of IV therapy: 400 mg PO daily

This protocol ensures appropriate therapeutic levels are maintained during the transition while accounting for the approximately 50% bioavailability of oral amiodarone compared to IV administration 2.

Loading and Maintenance Considerations

For patients requiring long-term oral amiodarone therapy after IV administration:

• Loading phase: Continue the appropriate oral dose (based on duration of prior IV therapy) until a total cumulative dose of 10 g has been administered
• Maintenance phase: After completing the loading phase, reduce to 200-400 mg PO daily 1

Administration Considerations

When switching from IV to oral amiodarone:

• Avoid grapefruit juice during oral amiodarone therapy as it inhibits CYP3A-mediated metabolism, resulting in increased plasma levels 2
• Consider using a central venous catheter for IV administration when concentrations exceed 2 mg/mL to avoid phlebitis 2
• Monitor for QT prolongation, bradycardia, and AV block during the transition period 3

Monitoring Requirements

Regular monitoring is essential during amiodarone therapy:

• ECG monitoring for QT prolongation and conduction abnormalities
• Thyroid function tests every 6 months
• Liver function tests every 6 months
• Pulmonary evaluations every 6 months 3

Common Pitfalls to Avoid

1. Underdosing during transition: Failure to account for the lower bioavailability of oral amiodarone (approximately 50%) compared to IV administration
2. Inadequate loading: Not providing sufficient loading dose before transitioning to maintenance dosing
3. Medication interactions: Not adjusting doses of concurrent medications that interact with amiodarone (particularly warfarin, digoxin, statins)
4. Insufficient monitoring: Failing to monitor for adverse effects during the transition period

By following these evidence-based guidelines for transitioning from IV to oral amiodarone, clinicians can maintain therapeutic efficacy while minimizing the risk of adverse effects.