According to the Vaughan Williams classification, amiodarone is primarily classified as a Class III antiarrhythmic. However, it also has additional actions including:
- A Class I (sodium channel block), Class II (β-blockade), and Class IV (calcium channel block) properties in addition to Class III potassium channel block ✓
- B Adenosine receptor agonism and phosphodiesterase inhibition
- C Direct activation of the vagus nerve increasing AV nodal refractory period
- D Selective IK1 (inward rectifier) potassium channel blockade only
Correct answer: A. Class I (sodium channel block), Class II (β-blockade), and Class IV (calcium channel block) properties in addition to Class III potassium channel block
Explanation
Amiodarone is a multi-channel blocker with properties spanning all four Vaughan Williams classes: it blocks IKr and IKs (Class III, prolongs QT), voltage-gated Na+ channels (Class I), has non-competitive β-blocking effects (Class II), and blocks L-type Ca2+ channels (Class IV). This 'dirty drug' profile makes it effective for diverse arrhythmias but also underlies its extensive side-effect profile (thyroid, pulmonary, hepatic, corneal, skin).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.