NAPLEX (North American Pharmacist Licensure Examination) Practice Exam 2025 - Free NAPLEX Practice Questions and Study Guide

Antiarrhythmics are the correct choice as the medication group associated with a markedly prolonged QT interval when it is greater than 500 ms. Antiarrhythmic medications, especially those belonging to class III (e.g., amiodarone, sotalol), are commonly known for their potential to prolong the QT interval on an electrocardiogram (ECG). Prolongation of the QT interval can predispose patients to a type of arrhythmia known as Torsades de Pointes, which can be life-threatening. Monitoring the QT interval and adjusting medication regimens accordingly is crucial in patients taking antiarrhythmic drugs to prevent adverse cardiac events.

Antihypertensives, antidiabetics, and antibiotics are not typically associated with marked QT prolongation as compared to antiarrhythmic medications. While some medications from these groups may have a mild effect on the QT interval, the risk is significantly higher with antiarrhythmics.