DC Pharmacology & Drug Administration 2 — Questions and Answers
Question 1: A patient in atrial fibrillation is started on digoxin. Which electrolyte imbalance most increases the risk of digoxin toxicity?
- Hypernatremia
- Hypokalemia (Correct answer)
- Hypermagnesemia
- Hypercalciuria
Correct answer: Hypokalemia
Hypokalemia potentiates digoxin toxicity by increasing binding of digoxin to cardiac Na+/K+-ATPase.
Question 2: Which of the following best describes the mechanism of adenosine when used to treat supraventricular tachycardia (SVT)?
- Blocks sodium channels to slow conduction
- Transiently blocks AV node conduction via A1 receptor activation (Correct answer)
- Prolongs the QT interval to terminate reentry
- Activates beta-2 receptors to slow the sinus node
Correct answer: Transiently blocks AV node conduction via A1 receptor activation
Adenosine activates cardiac A1 receptors, transiently hyperpolarizing AV nodal cells and interrupting reentrant SVT circuits.
Question 3: A patient receiving IV amiodarone develops hypotension. The MOST likely cause is:
- Hyperkalemia from potassium-sparing effects
- Vasodilation from the polysorbate 80 vehicle (Correct answer)
- Reflex tachycardia from direct cardiac stimulation
- QT prolongation leading to torsades de pointes
Correct answer: Vasodilation from the polysorbate 80 vehicle
IV amiodarone formulations contain polysorbate 80 and benzyl alcohol, which cause vasodilation and hypotension during rapid infusion.
Question 4: Procainamide is preferred over lidocaine for treatment of which rhythm in the setting of WPW syndrome?
- Atrial flutter with slow ventricular response
- Ventricular fibrillation
- Atrial fibrillation with rapid ventricular response via accessory pathway (Correct answer)
- Sinus bradycardia
Correct answer: Atrial fibrillation with rapid ventricular response via accessory pathway
Procainamide slows conduction in the accessory pathway, making it preferred over AV nodal blockers (which can accelerate conduction through the bypass tract) in WPW with AF.
Question 5: Which antiarrhythmic drug is contraindicated in patients with structural heart disease due to its proarrhythmic risk demonstrated in the CAST trial?
- Amiodarone
- Sotalol
- Flecainide (Correct answer)
- Mexiletine
Correct answer: Flecainide
The CAST trial showed that flecainide (a Class IC drug) increased mortality in patients with structural heart disease by suppressing ventricular ectopy but increasing the risk of fatal arrhythmias.
Question 6: Magnesium sulfate is the first-line treatment for torsades de pointes primarily because it:
- Shortens the QT interval by blocking calcium channels
- Suppresses afterdepolarizations by stabilizing the cell membrane (Correct answer)
- Converts the rhythm to sinus by activating the sinoatrial node
- Increases heart rate to overdrive-suppress the ectopic focus
Correct answer: Suppresses afterdepolarizations by stabilizing the cell membrane
Magnesium suppresses early afterdepolarizations (EADs) that trigger torsades de pointes by stabilizing cardiac membranes, even without significantly shortening the QT interval.
Question 7: A patient receives 300 mg of IV amiodarone over 10 minutes for stable wide-complex tachycardia. What is the MOST important parameter to monitor during this infusion?
- Serum creatinine
- Blood pressure (Correct answer)
- Serum potassium
- Respiratory rate
Correct answer: Blood pressure
Rapid IV amiodarone infusion causes vasodilation and can produce profound hypotension, making blood pressure the most critical parameter to monitor.
DC Pharmacology & Drug Administration 2
A patient in atrial fibrillation is started on digoxin.
Which electrolyte imbalance most increases the risk of digoxin toxicity?