Amiodarone
Summary
Class III antiarrhythmic (K+ channel blocker) that also has class I, II, and IV properties. First-line for ventricular arrhythmias and rate/rhythm control of atrial fibrillation; notorious for multi-organ toxicity.
Detail
Amiodarone primarily blocks K+ channels, prolonging phase 3 repolarization and the action potential duration (class III), but also blocks Na+ channels (class I), beta receptors (class II), and Ca2+ channels (class IV). Half-life is extremely long (~58 days) due to extensive lipophilic tissue distribution. Indications: ventricular tachycardia/fibrillation (ACLS), atrial fibrillation rhythm control. Toxicities (check PFTs, LFTs, TFTs): pulmonary fibrosis, hepatotoxicity, thyroid dysfunction (both hypo- and hyperthyroidism — iodine-rich), corneal microdeposits, blue-gray skin discoloration ('smurf skin'), peripheral neuropathy, photosensitivity, QT prolongation (but rare torsades). Boards: 'fibrosis + bluish skin + thyroid abnormality' = amiodarone.
Sources
- First Aid for USMLE Step 1 2024
- Sketchy Pharmacology
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