ATC Group: C01BA Antiarrhythmics, class Ia

Ajmaline is a class Ia antiarrhythmic agent that apparently acts by changing the shape and threshold of cardiac action potentials. It produces potent sodium channel blocking effects and a very short half-life which makes it a very useful drug for acute intravenous treatments. The drug has been very popular in some countries for the treatment of atrial fibrillation in patients with the Wolff–Parkinson–White syndrome and in well tolerated monomorphic ventricular tachycardias. It has also been used for many years as a drug to challenge the conduction system of the heart in cases of bundle branch block and syncope. In these cases, abnormal prolongation of the HV interval has been taken as a proof for infrahisian conduction defects tributary for permanent pacemaker implantation.

Disopyramide is a myocardial depressant and has anti-cholinergic effects. It decreases membrane responsiveness, prolongs the effective refractory period (ERP) and slows automaticity in cells with augmented automaticity.

Hydroquinidine is a d-rotatory alkaloid derived from cinchiona bark. Hydroquinidine is a pharmaceutical agent that acts as a class I antiarrhythmic agent (Ia) in the heart. Hydroquinidine causes increased action potential duration, as well as a prolonged QT interval. Like all other class I antiarrhythmic agents, hydroquinidine primarily works by blocking the fast inward sodium current (INa). Hydroquinidine is also used for the treatment of Malaria.

Procainamide is a Group 1A cardiac antiarrhythmic drug. Procainamide (PA) increases the effective refractory period of the atria, and to a lesser extent the bundle of His-Purkinje system and ventricles of the heart. It reduces impulse conduction velocity in the atria, His-Purkinje fibers, and ventricular muscle, but has variable effects on the atrioventricular (A-V) node, a direct slowing action and a weaker vagolytic effect which may speed A-V conduction slightly.

Quinidine increases plasma levels of dextromethorphan by competitively inhibiting cytochrome P450 2D6 (CYP2D6), which catalyses a major biotransformation pathway for dextromethorphan.