Oral Amiodarone Dosing After IV Drip for VT During Catheterization
After IV amiodarone for VT during catheterization, start oral amiodarone at 800-1,600 mg daily in divided doses (typically 400-800 mg twice daily) until a cumulative total of 10 grams is reached, then transition to maintenance dosing of 200-400 mg daily. 1
Dosing Algorithm Based on Duration of IV Therapy
The oral dose you select depends critically on how long the patient received IV amiodarone 1:
- IV therapy <1 week: Start 800-1,600 mg oral daily 1
- IV therapy 1-3 weeks: Start 600-800 mg oral daily 1
- IV therapy >3 weeks: Start 400 mg oral daily 1
Since most patients receiving amiodarone during catheterization for acute VT will have received IV therapy for less than 1 week, the 800-1,600 mg daily loading dose is most appropriate 1.
Loading Phase Details
- Divide the daily dose into 2-3 administrations to improve tolerance 1
- Continue loading dose until cumulative total of 10 grams is administered 1
- Morning administration is preferred to allow better monitoring of cardiovascular side effects like bradycardia and QT prolongation during waking hours 2
- Onset of oral effect occurs within days, though full antiarrhythmic effect may take 1-3 weeks 1
Transition to Maintenance Dosing
After achieving the 10-gram cumulative loading dose 1:
- Reduce to 200-400 mg daily for maintenance 1, 2
- Use the lowest effective dose to minimize adverse effects, which correlate directly with total amiodarone exposure 1, 2
- Standard maintenance is typically 200 mg daily for most patients 2
Critical Monitoring During Transition
Bradycardia risk is particularly important in your patient who just received IV amiodarone during catheterization 3:
- Drug-related bradycardia occurs in 4.9% of patients receiving IV amiodarone 3
- Monitor heart rate continuously during the transition period 3
- If heart rate drops by 10 bpm or more, reduce the oral dose 3
- Second- or third-degree heart block is an absolute contraindication to continued therapy without pacemaker 3
Important Drug Interactions to Address Immediately
Before starting oral amiodarone 3:
- Reduce digoxin dose by 50% if patient is taking it, as amiodarone predictably doubles digoxin levels 3
- Monitor INR at least weekly for 6 weeks if patient takes warfarin, as amiodarone significantly increases anticoagulation 3
- Assess all AV nodal blocking agents (beta-blockers, calcium channel blockers) for additive bradycardia risk 3
Common Pitfalls to Avoid
- Don't use maintenance dosing initially - the loading phase is essential for achieving therapeutic effect quickly given amiodarone's long half-life 1
- Don't forget to counsel about grapefruit - patients must avoid grapefruit juice entirely as it inhibits metabolism and increases plasma levels 3
- Don't ignore the narrow therapeutic window - amiodarone requires close monitoring due to potential for serious adverse effects including pulmonary toxicity, thyroid dysfunction, and hepatic toxicity 1, 2
- Don't assume electrophysiologic study results predict clinical success - even when VT remains inducible on amiodarone, many patients (80 out of 101 in one study) remain arrhythmia-free clinically 4
Adverse Effect Surveillance
Most common adverse effects to monitor 1, 5:
- Bradycardia and QT prolongation (check ECG regularly) 1
- Tremor or ataxia (35% of patients) 5
- Pulmonary toxicity presenting as subacute cough and progressive dyspnea with interstitial infiltrates on chest X-ray 1
- Thyroid dysfunction (6% of patients) 5
- GI upset and constipation 1
Frequency of adverse effects correlates with total exposure, so aggressive loading followed by the lowest effective maintenance dose is the optimal strategy 1, 2.