Class 3 Antiarrhythmics (Amiodarone, Sotalol, Dofetilide, Ibutilide) Flashcards
What is the primary mechanism of action of Class III antiarrhythmics?
Block potassium channels, prolonging phase two and phase three of the cardiac action potential, thereby increasing the refractory period.
Which phases of the cardiac action potential are affected by Class III antiarrhythmics?
Phase two, which is the calcium plateau, and phase three, which is potassium repolarization.
What are the primary indications for Class III antiarrhythmics?
Rhythm control for supraventricular and ventricular arrhythmias, including atrial fibrillation, atrial flutter, and ventricular tachycardia.
What is the most notible side effect of all the Class III antiarrhythmics?
Prolongation of the QT interval, increasing the risk of torsades de pointes.
What are the main Class III antiarrhythmic drugs?
Amiodarone, dofetilide, ibutilide, and sotalol.
Which Class III antiarrhythmic has the lowest risk of causing torsades de pointes?
Amiodarone has the lowest risk compared to dofetilide, ibutilide, and sotalol.
What distinguishes amiodarone from other Class III antiarrhythmics?
Amiodarone has additional Class I, which is sodium channel blockade, Class II, which is beta-blocking, and Class IV, which is calcium channel blocking effects.
What are the Class I effects of amiodarone?
Inhibits fast sodium channels, slowing phase zero ventricular depolarization and prolonging QRS duration.
What are the Class II effects of amiodarone?
Beta-blockade, inhibiting sympathetic stimulation and slowing sinus node and atrioventricular nodal conduction, leading to a prolonged PR interval.
What are the Class IV effects of amiodarone?
Inhibits slow L-type calcium channels, prolonging atrioventricular nodal conduction and reducing heart rate.
What are the expected ECG changes with amiodarone?
Prolonged PR interval, prolonged QRS duration, prolonged QT interval, and decreased sinus rate.
What is the most serious pulmonary side effect of amiodarone?
Pulmonary fibrosis, which can lead to restrictive lung disease.
What are the neurological side effects of amiodarone?
Tremors, ataxia, and sleep disturbances.
How does amiodarone affect the thyroid?
It can cause both hyperthyroidism and hypothyroidism due to its iodine content.
What are the dermatologic side effects of amiodarone?
Blue-gray skin discoloration and photodermatitis (sun sensitivity).
What are the cardiovascular side effects of amiodarone?
Heart block and potential worsening of heart failure.
What hepatic toxicity is associated with amiodarone?
Hepatitis, which can manifest with elevated liver enzymes.
How does amiodarone affect the eyes?
Corneal microdeposits, which are usually asymptomatic but may cause visual disturbances.
How does amiodarone interact with the cytochrome P450 system?
Amiodarone inhibits cytochrome P450 enzymes, particularly CYP3A4, leading to increased levels of drugs metabolized by this system.
Which drugs have significant interactions with amiodarone due to CYP450 inhibition?
Warfarin, which increases the anticoagulation effect, digoxin, which increases toxicity risk, and statins, which increase the risk of myopathy.
What is the primary clinical use of dofetilide and ibutilide?
Treatment of atrial fibrillation and atrial flutter by prolonging the refractory period.
Which Class III antiarrhythmic has beta-blocking properties?
Sotalol, which has both potassium channel-blocking and beta-blocking effects.
Which Class III antiarrhythmic is most commonly used in ventricular arrhythmias?
Amiodarone, due to its broad-spectrum antiarrhythmic effects and lower risk of torsades de pointes.
