<prompt> Select the most suitable antiarrhythmic drug for counteracting ventricular extrasystoles due to digoxin toxicityVerapamilQuinidineLignocaineAmiodarone  <response>: Digitalis Toxicity:- Toxicity of digitalis is high, margin of safety is low therapeutic index 1.5-3. Higher cardiac moality has been repoed among patients with steady-state plasma digoxin levels 1.1 ngml but still within the therapeutic range during maintenance therapy. Manifestations and treatment of toxicity For ventricular arrhythmias:- Lidocaine i.v. repeated as required is the drug of choice. It suppresses the excessive automaticity, but does not accentuate A-V block. Quinidine, procainamide and propafenone are contraindicated. Ref:- kd tripathi; pg num:-516 