Which of the following is classified as a Class 1B antiarrhythmic drug?

Lidocaine is classified as a Class 1B antiarrhythmic drug primarily because of its mechanism of action and its specific use in the treatment of cardiac arrhythmias, particularly ventricular arrhythmias. Class 1B agents work by blocking sodium channels in the heart, which helps to stabilize the cardiac cell membrane during depolarization. They are especially effective during depolarization phases and have a preference for damaged or ischemic myocardial tissue, which makes them particularly useful in acute situations such as ventricular tachycardia in emergency settings.

In addition, Class 1B agents like Lidocaine are characterized by a rapid association and dissociation from the sodium channels, which makes them well-suited for their role in acute management of arrhythmias. Lidocaine's efficacy and safety profile in these scenarios, particularly in intravenous formulations, emphasizes its classification within this category.

The other choices, while they are antiarrhythmic drugs, fall under different classifications. For instance, Flecainide and Moricizine are Class 1C agents, which have a stronger effect on conduction in the His-Purkinje system and are used for different types of arrhythmias, often with specific indications related to atrial fibrillation and