Drugs belonging to this group are, with a few rare exceptions, local anesthetics which form complexes with lipoproteins of cell membranes of the myocardia, thus blocking Na+ channel conductivity and the flow of Na+ into the cell, and facilitate the release of K+ from myocardial cells, which as a result leads to a weak suppression of depolarization of myocardial cells, reduction of repolarization time, and a slowing of the propagation of excitation. This series of drugs prolongs action potentials and increases the effective refractory period of the myocardium. Automatism of ectopic centers is suppressed in the myocardium, primarily in the ventricles.
Drugs of this subgroup slow down the speed of transmitting excitation, reduce excitability of Purkinje fibers, suppress automatism of ectopic regions and increase the effective refractory period. They exhibit direct and mediated anticholinergic action. The antiar-rhythmic drugs quinidine, procainamide, and disopyramide belong to this subgroup. Drugs of this subgroup are used for treating irregular sinus rhythm, paroxysmal, supraven-tricular, and ventricular arrythmia, preventing arterial fibrillation, and premature heartbeats.
Quinidine: Quinidine, (5-vinyl-2-quinyclidinyl)-(6-methyoxy-4-quinolyl)-methanol (18.1.1) is the dextro-isomer of the alkaloid quinine and is one of the four most important alkaloids, which are isolated from the bark of the cinchona tree [1-3]. Quinidine is a secondary alcohol, the radicals in which are a 5-methyoxyquinoline ring and 3-vinylquinuclidine. Quinidine only differs from quinine in the configuration of the carbon atom of the carbinol group, and it can be made by isomerization of quinine (220.127.116.11) . Quinidine is proposed to synthesize by different ways [5-7].
Quinidine exhibits all of the pharmacological properties of quinine, including antimalarial, fever-reducing, and other properties. Quinidine is used in various forms of arrhythmia for preventing tachycardia and atrial fibrillation, and particularly for preventing ciliary fibrillation, paroxysmal supraventricular tachycardia, extrasystole, and ventricular tachycardia. However, it is a toxic drug and is used relatively rarely.
It is also prescribed under the name cardioquin, duraquin, quinidex, and others.
Procainamide: Procainamide, 4-amino-N-[2-(diethylamino)ethyl]benzamide (18.1.3), is synthesized by reacting 4-nitrobenzoic acid chloride with N,N-diethylethylendiamine and subsequent reduction of the nitro group of the resulting 4-nitro-N-[2-(diethylamino)ethyl]ben-zamide (18.1.2) into an amino group [8,9].
C2H5 c2h5 o2n^ co-cl + h2n-ch2-ch2-n< -o2n ^ v—co-nh—ch2-ch2-n(
C2H5 18.1.2 c2h5
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