Amiodarone Toxicity Monitoring Workup
For patients on amiodarone, send thyroid studies (TSH and free T4), liver transaminase levels (ALT/AST), chest radiograph, and pulmonary function tests with DLCO at baseline and every 6 months, along with digoxin levels and PT/INR if the patient is taking these medications. 1, 2
Baseline Assessment (Before Starting Amiodarone)
The American Academy of Family Physicians recommends comprehensive baseline testing before initiating amiodarone therapy 1, 2:
- Thyroid function tests: TSH and free T4 1
- Liver function tests: ALT and AST (transaminase levels) 1
- Chest radiograph 1, 2
- Pulmonary function tests: Including DLCO (diffusing capacity of lung for carbon monoxide) 1, 2
- Ophthalmologic examination: Only if preexisting visual impairment exists 1
- Digoxin level: If patient is taking digoxin 1
- PT/INR: If patient is taking warfarin 1
Every 6-Month Monitoring
The following tests should be repeated every 6 months during amiodarone therapy 1, 2:
- Thyroid studies (TSH; if abnormal, add free T4) 1, 2
- Liver transaminase levels (ALT/AST) 1, 2
- Digoxin level if patient is on digoxin 1
During Loading Phase
Close surveillance of heart rate is essential, especially during the first week of treatment 1. Monitor for bradycardia and heart block, which occur in 1-3% of patients 1.
For patients on warfarin, monitor PT/INR at least once weekly during the first 6 weeks of amiodarone therapy, as amiodarone increases prothrombin time by 100% after 3-4 days 1, 3.
Symptom-Triggered Testing
Pulmonary Symptoms
Any patient reporting new or worsening dyspnea or cough requires immediate assessment 1, 2. This is critical because pulmonary toxicity is the most serious adverse effect and can progress rapidly 1. Send:
- Chest radiograph (looking for patchy interstitial infiltrates) 1
- Pulmonary function tests with DLCO 1
- High-resolution CT scanning if diagnosis remains unclear 1
Important caveat: Routine screening has limited value for detecting pulmonary toxicity early, as it can develop rapidly with no antecedent abnormalities 1, 2. Rule out congestive heart failure first, as it can mimic amiodarone pneumonitis 1, 2.
Visual Changes
Any patient reporting changes in visual acuity or peripheral vision requires immediate ophthalmologic referral 1, 2. While corneal microdeposits occur in nearly all patients and rarely affect vision, optic neuropathy can progress to blindness 1.
New Arrhythmias
If new arrhythmias develop, check thyroid function immediately 3. Hyperthyroidism is best identified by elevated free T4, elevated T3, and suppressed TSH 3. Arrhythmia breakthroughs may accompany amiodarone-induced thyrotoxicosis 3.
Drug Interaction Monitoring
For patients on digoxin: Amiodarone increases digoxin levels by 70% after one day 3. Reduce digoxin dose by 50% when starting amiodarone and monitor levels closely 1.
For patients on high-dose statins (simvastatin >20 mg/day, atorvastatin >20 mg/day, lovastatin >40 mg/day): Monitor for myopathy/rhabdomyolysis symptoms, as amiodarone inhibits CYP3A4 and increases statin levels 3.
For patients on other antiarrhythmics (quinidine, procainamide, flecainide): Monitor drug levels and reduce doses by one-third to one-half 3.
Critical Decision Points
Discontinue amiodarone if 1, 2:
- Liver enzymes exceed 3 times normal (unless patient has life-threatening arrhythmia risk)
- Pulmonary toxicity is confirmed
- Symptomatic thyroid dysfunction develops that cannot be managed
The evidence strongly supports this structured monitoring approach, with pharmacist-managed programs demonstrating significantly improved monitoring rates (OR=8.13 for TSH testing, OR=5.89 for PFTs) and potential cost savings of $2.14 per dollar spent 4. Recent case reports emphasize that multi-organ toxicity can occur simultaneously, affecting liver, lungs, thyroid, and eyes 5, 6, reinforcing the need for comprehensive monitoring across all organ systems.