Which of the following is NOT a Class 1B drug?

Atenolol is classified as a beta-blocker, specifically a Class II antiarrhythmic drug, whereas Class 1B drugs primarily consist of sodium channel blockers that are often used to treat ventricular arrhythmias. Lidocaine, Mexiletine, and Phenytoin all fall under Class 1B, as they are effective in stabilizing cardiac membranes and reducing excitability of the heart muscle by inhibiting sodium channels.

By confirming that Atenolol does not belong to Class 1B, it highlights the distinction in drug classifications used in treating arrhythmias, thereby reinforcing key pharmacological concepts for students studying this area. Understanding these classifications is crucial for effective treatment of patients with arrhythmias and for making informed clinical decisions.