DC Pharmacology & Drug Administration 3 — Questions and Answers
Question 1: Which Class III antiarrhythmic drug has both beta-blocking and potassium channel-blocking properties?
- Amiodarone
- Sotalol (Correct answer)
- Dofetilide
- Ibutilide
Correct answer: Sotalol
Sotalol is unique in that it combines non-selective beta-blockade (Class II) with potassium channel blockade (Class III), prolonging the action potential duration.
Question 2: When atropine is administered to a patient with symptomatic bradycardia, its primary mechanism is:
- Direct stimulation of beta-1 adrenergic receptors in the SA node
- Competitive antagonism of muscarinic (M2) receptors, removing vagal inhibition (Correct answer)
- Blocking potassium channels to shorten the refractory period
- Increasing intracellular calcium to enhance automaticity
Correct answer: Competitive antagonism of muscarinic (M2) receptors, removing vagal inhibition
Atropine competitively blocks muscarinic M2 receptors, removing parasympathetic (vagal) inhibition and thereby increasing heart rate.
Question 3: Ibutilide (Corvert) is FDA-approved primarily for:
- Long-term maintenance of sinus rhythm after cardioversion
- Acute pharmacologic cardioversion of recent-onset atrial fibrillation or flutter (Correct answer)
- Rate control in chronic atrial fibrillation
- Suppression of ventricular ectopy post-MI
Correct answer: Acute pharmacologic cardioversion of recent-onset atrial fibrillation or flutter
Ibutilide is a Class III antiarrhythmic approved for rapid pharmacologic conversion of atrial fibrillation or flutter of recent onset (within 7 days).
Question 4: A patient in stable VT receives lidocaine 1.5 mg/kg IV bolus with no effect. The correct next step regarding lidocaine is:
- Stop lidocaine and immediately switch to amiodarone
- Give an additional 0.5–0.75 mg/kg IV bolus and reassess (Correct answer)
- Double the original bolus dose and repeat
- Start a lidocaine infusion without additional bolus doses
Correct answer: Give an additional 0.5–0.75 mg/kg IV bolus and reassess
Current ACLS guidelines allow repeat lidocaine boluses of 0.5–0.75 mg/kg IV every 5–10 minutes (max 3 mg/kg total) if the initial bolus is ineffective.
Question 5: Which of the following is a pharmacologic effect UNIQUE to dronedarone compared to amiodarone?
- It blocks sodium, potassium, and calcium channels
- It lacks iodine moieties, reducing thyroid and pulmonary toxicity (Correct answer)
- It prolongs the QT interval significantly
- It requires loading doses before reaching therapeutic effect
Correct answer: It lacks iodine moieties, reducing thyroid and pulmonary toxicity
Dronedarone was developed as a non-iodinated analog of amiodarone, eliminating thyroid and pulmonary toxicities, though it is less effective and contraindicated in heart failure.
Question 6: Dopamine at a dose of 5–10 mcg/kg/min is used in hemodynamically unstable bradycardia primarily because it:
- Blocks muscarinic receptors to reduce vagal tone
- Stimulates beta-1 and dopaminergic receptors to increase heart rate and contractility (Correct answer)
- Directly activates the SA node via calcium channel stimulation
- Reduces afterload, allowing the heart to beat faster reflexively
Correct answer: Stimulates beta-1 and dopaminergic receptors to increase heart rate and contractility
At 5–10 mcg/kg/min, dopamine predominantly stimulates beta-1 receptors, increasing heart rate and cardiac output in hemodynamically unstable bradycardia.
Question 7: A patient with a known sulfa allergy asks about dofetilide therapy. The correct counseling is:
- Dofetilide is a sulfonamide and is absolutely contraindicated
- Dofetilide is not a sulfonamide; the sulfa allergy is not a direct contraindication (Correct answer)
- A sulfa allergy requires a 50% dose reduction of dofetilide
- An antihistamine premedication should be given before each dofetilide dose
Correct answer: Dofetilide is not a sulfonamide; the sulfa allergy is not a direct contraindication
Dofetilide is a methanesulfonamide, not a sulfonamide antibiotic; cross-reactivity with sulfa drug allergies has not been established, so it is not contraindicated.
DC Pharmacology & Drug Administration 3
Which Class III antiarrhythmic drug has both beta-blocking and potassium channel-blocking properties?