Screening Requirements for Chronic Amiodarone Therapy
Patients on chronic amiodarone require baseline comprehensive assessment followed by thyroid and liver function testing every 6 months, with additional surveillance for pulmonary, cardiac, ophthalmologic, and neurologic toxicity based on symptoms. 1, 2
Baseline Assessment (Before Starting Amiodarone)
Required for all patients:
- Complete history and physical examination focusing on heart failure symptoms, arrhythmia manifestations, and current medications 1
- Chest radiograph 1
- Pulmonary function tests including diffusing capacity of lung for carbon monoxide (DLCO) 1, 2
- Thyroid studies (TSH, free T4) 1, 3
- Liver transaminase levels (ALT, AST, GGT) 1, 4
- Electrocardiogram 1
- Renal function and complete blood count 5
- Ophthalmologic examination only if preexisting visual impairment exists 1
If taking specific medications:
Every 6 Months Monitoring (Routine)
Mandatory laboratory surveillance:
- Thyroid studies (TSH, free T4) 1, 2, 3
- Liver transaminase levels 1, 2, 3
- Digoxin level if patient continues taking digoxin 1
Clinical assessment:
- History and physical examination directed at detecting anticipated adverse effects, specifically asking about dyspnea, cough, visual changes, tremor, ataxia, and skin changes 1
- Heart rate assessment 1
Symptom-Triggered Assessments
Pulmonary symptoms (dyspnea, cough):
- Immediate chest radiograph 1
- Pulmonary function tests including DLCO 1
- Do not delay assessment—pulmonary toxicity can progress rapidly and is the most serious adverse effect 2, 3, 6
- Rule out congestive heart failure before attributing symptoms to amiodarone toxicity 3, 6
Visual symptoms (changes in acuity or peripheral vision):
- Immediate ophthalmologic examination 1
- Optic neuropathy/neuritis can progress to permanent blindness 1, 4
During warfarin coadministration:
- Monitor INR at least weekly during first 6-7 weeks of combined therapy, as peak interaction effects occur at 7 weeks 1, 3
- Warfarin clearance is reduced, causing sudden and pronounced INR increases 1
Special Monitoring Considerations
Drug interaction surveillance:
- Amiodarone inhibits CYP2C9, CYP2D6, and CYP3A4 pathways 1, 2
- Reduce digoxin dose by 50% immediately when starting amiodarone, as levels predictably double 1, 3
- Monitor for toxicity from statins, beta blockers, calcium channel blockers, and other antiarrhythmics 2
Cardiovascular monitoring:
- Close heart rate surveillance especially during first week of treatment 1, 2
- Bradycardia and heart block occur in 1-3% of patients on oral amiodarone 1, 2
- QTc prolongation occurs frequently but torsades de pointes is rare (less than 2%) 4
Critical Pitfalls to Avoid
- Never delay pulmonary assessment when patients report new dyspnea or cough—pulmonary toxicity presents as subacute cough and progressive dyspnea with patchy interstitial infiltrates and reduced DLCO, and can progress to ARDS at approximately 1% annually 1, 2, 3, 6
- Do not rely solely on routine screening tests for pulmonary toxicity—it can develop rapidly with no antecedent abnormalities on chest radiographs or pulmonary function tests 6
- Discontinue amiodarone if liver transaminases exceed three times upper limit of normal unless life-threatening arrhythmia risk exists with no alternative options 2, 3
- Corneal microdeposits occur in nearly all patients but seldom affect vision and rarely require discontinuation 1
- Hypothyroidism (2-4 times more common than hyperthyroidism) allows continuation of amiodarone with levothyroxine replacement 2, 3
- Neurologic toxicity (ataxia, paresthesias, tremor) is often dose-related and improves with dose reduction; peripheral neuropathy occurs at 0.3% annually 1, 2