A patient is administered lidocaine for the treatment of an arrhythmia. Which of the following, if present, will increase the effects of this drugs?
A) Hypoxemia
(B) Anemia
(C) Exercise
(D) Bradycardia
(E) Liver failure
1 Answer
Answer C (correct answer): Flecainide is a class Ic antiarrhythmic that blocks cardiac sodium channels. This drug exhibits “use dependence” meaning drug binding to sodium channels increases at fast heart rates as explained in the video. For this reason, flecainide toxicity is most likely to occur during exercise.
Through blockade of sodium channels, flecainide may prolong the QRS interval. Significant QRS prolongation is an indication to stop the drug due to high risk of toxicity. Patients started on flecainide are usually referred for a cardiac stress test to evaluate the QRS interval during exercise. If the QRS interval prolongs with exercise, the patient is at increased risk for flecainide toxicity.
Answers A and B (incorrect answers): Hypoxemia and anemia do not increase the likelihood of flecainide toxicity.
Answer D (incorrect answer): Bradycardia will make flecainide toxicity less likely.
Answer E (incorrect answer): Flecainide is renally excreted. Liver failure does not significantly alter the likelihood of flecainide toxicity.