66-year-old female with paroxysmal atrial fibrillation is started on dofetilide to maintain sinus rhythm. Her physician hospitalizes her for the first three days of therapy. During this time, monitoring which of the following is most important?
A) serum drug levels
B)Heart Rate
C)Renal Function
D) QT interval
E) Blood Pressure
Answer D (correct answer): Dofetilide is a class III antiarrhythmic drug that blocks potassium channels. Like all potassium channel blockers, it can prolong the QT interval on ECG. If QT prolongation is excessive, Torsades de Pointes may occur which can be life-threatening. For this reason, QT interval monitoring is often done in the hospital when initiating therapy with dofetilide (this is also done with sotalol, another class III drug).
Answer A (incorrect answer): Serum drugs levels of dofetilide are not routinely monitored.
Answer B (incorrect answer): Heart rate can alter the risk of toxicity with dofetilide. This drug displays “reverse use dependence” meaning the drug exhibits enhanced potassium channel binding at lower heart rates. The risk of QT prolongation is greater at slower heart rates but QT prolongation may also occur at normal heart rates. Although monitoring of the heart rate is important, the QT interval is the best answer and the most important parameter among patients on dofetilide.
Answer C (incorrect answer): Dofetilide dosing must be adjusted for renal function. However, this is not the reason for hospitalization and monitoring during the first few days of therapy.
Answer E (incorrect answer): It is not necessary to monitor blood pressure when starting dofetilide.