procainamide

Absorption

75 to 95%

Toxicity

LD50=95 mg/kg (rat, IV); LD50=312 mg/kg (mouse, oral); LD50=103 mg/kg (mouse, IV); LD50=250 mg/kg (rabbit, IV)

Description

Procainamide and its analogs were employed by Dr Claude Beck in a series of cardiac surgeries during the early 1930s. The compound was used to alleviate arrhythmias that present during the procedures, and was selected for its favorable tissue absorption properties. Procainamide’s central amide provides it protection from inactivating esterase action and allows oral administration of the compound. Procainamide was approved for use in the United States in 1950.

The Uses of procainamide

Procainamide is intended for treating paroxysmal atrial tachycardia, atrial fibrillation, premature ventricular contraction, and ventricular tachycardia. For quickly reaching therapeutic concentrations, parenternal introduction of procainamide is preferred over cynidine.

The Uses of procainamide

Procainamide is used in the management of atrial and ventricular tachydysrhythmias.

Indications

For the treatment of life-threatening ventricular arrhythmias.

Background

A derivative of procaine with less CNS action.

Definition

ChEBI: 4-Aminobenzamide substituted on the amide N by a 2-(diethylamino)ethyl group. It is a pharmaceutical antiarrhythmic agent used for the medical treatment of cardiac arrhythmias.

Biological Functions

Procainamide (Pronestyl, Procan SR) is a derivative of the local anesthetic agent procaine. Procainamide has a longer half-life, does not cause CNS toxicity at therapeutic plasma concentrations, and is effective orally. Procainamide is a particularly useful antiarrhythmic drug, effective in the treatment of supraventricular, ventricular, and digitalis-induced arrhythmias.

Synthesis Reference(s)

Synthesis, p. 714, 1975 DOI: 10.1055/s-1975-23900

Mechanism of action

The chemical difference between procainamide and procaine lies in the replacement of the ester group with an amide group. The action of procainamide is qualitatively similar to the action of procaine. Its effect on the heart is identical to that of quinidine. As an antiarrhythmic, procainamide is preferred over procaine because unlike procaine, it is better absorbed when taken orally and it is more difficult for the esterases of the plasma to hydrolyze it, which results in long-lasting action.

Pharmacokinetics

Procainamide is an agent indicated for production of local or regional anesthesia and in the treatment of ventricular tachycardia occurring during cardiac manipulation, such as surgery or catheterization, or which may occur during acute myocardial infarction, digitalis toxicity, or other cardiac diseases. The mode of action of the antiarrhythmic effect of Procainamide appears to be similar to that of procaine and quinidine. Ventricular excitability is depressed and the stimulation threshold of the ventricle is increased during diastole. The sinoatrial node is, however, unaffected.

Clinical Use

Procainamide is an effective antiarrhythmic agent when given in sufficient doses at relatively short (3–4 hours) dosage intervals. Procainamide is useful in the treatment of premature atrial contractions, paroxysmal atrial tachycardia, and atrial fibrillation of recent onset. Procainamide is only moderately effective in converting atrial flutter or chronic atrial fibrillation to sinus rhythm, although it has value in preventing recurrences of these arrhythmias once they have been terminated by direct current (DC) cardioversion.
Procainamide can decrease the occurrence of all types of active ventricular dysrhythmias in patients with acute myocardial infarction who are free from A-V dissociation, serious ventricular failure, and cardiogenic shock. About 90% of patients with ventricular premature contractions and 80% of patients with ventricular tachycardia respond to procainamide administration. Although the spectrum of action and electrophysiological effects of quinidine and procainamide are similar, the relatively short duration of action of procainamide has tended to restrict its use to patients who are intolerant of or unresponsive to quinidine.

Side Effects

Acute cardiovascular reactions to procainamide administration include hypotension, A-V block, intraventricular block, ventricular tachyarrhythmias, and complete heart block. The drug dosage must be reduced or even stopped if severe depression of conduction (severe prolongation of the QRS interval) or repolarization (severe prolongation of the QT interval) occurs.
Long-term drug use leads to increased antinuclear antibody titers in more than 80% of patients; more than 30% of patients receiving long-term procainamide therapy develop a clinical lupus erythematosus–like syndrome. The symptoms may disappear within a few days of cessation of procainamide therapy, although the tests for antinuclear factor and lupus erythematosus cells may remain positive for several months.
Procainamide, unlike procaine, has little potential to produce CNS toxicity. Rarely, patients may be confused or have hallucinations.

Synthesis

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]benzamide (18.1.2) into an amino group.

Drug interactions

The inherent anticholinergic properties of procainamide may interfere with the therapeutic effect of cholinergic agents. Patients receiving cimetidine and procainamide may exhibit signs of procainamide toxicity, as cimetidine inhibits the metabolism of procainamide. Simultaneous use of alcohol will increase the hepatic clearance of procainamide. Procainamide may enhance or prolong the neuromuscular blocking activity of the aminoglycosides with the potential of producing respiratory depression. The simultaneous administration of quinidine or amiodarone may increase the plasma concentration of procainamide.

Metabolism

Hepatic

Metabolism

Metabolites of procainamide include p-aminobenzoic acid and N-acetylprocainamide. Interestingly, the acetylated metabolite is also active as an antiarrhythmic. Its formation accounts for up to one-third of the administered dose and is catalyzed by the liver enzyme N-acetyl transferase. Because acetylation is strongly influenced by an individual's genetic background, marked variability in the amounts of this active metabolite may be observed from patient to patient. Renal excretion dominates, with approximately 90% of a dose excreted as unchanged drug and metabolites. The elimination half-life is approximately 3.5 hours. A substantial percentage (60–70%) of patients on procainamide show elevated levels of antinuclear antibodies after a few months. Of these patients, between 20 and 30% develop a drug-induced lupus syndrome if therapy is continued. These adverse effects, which are attributed to the aromatic amino group, are observed more frequently and more rapidly in “slow acetylators.” Usually, the symptoms associated with procainamide-induced lupus syndrome subside fairly rapidly after the drug is discontinued. These problems, however, have discouraged long-term procainamide therapy.

Toxicity evaluation

Procainamide is a class 1a antiarrhythmic that has a mechanism that resembles quinidine by binding to the transmembrane Nat channels and decreasing the number available for depolarization. This creates a delay of Nat entry into the cardiac myocyte during phase 0 of depolarization. As a result, the upslope of depolarization is slowed and the QRS complex widens. Procainamide may also affect phase 3 of the action potential, resulting in prolongation of repolarization and manifesting as QTc prolongation on the electrocardiogram (EKG). Unlike quinine, however, procainamide lacks alphablocking activity and quinidine’s vagolytic ability.
Vasodilation associated with procainamide toxicity (>10 mg ml°1) is due to interference with ganglionic transmission of catecholamine neurotransmitters and/or central nervous system (CNS) sympathetic inhibition. A reflex tachycardia may occur in response to this vasodilation. Rapid intravenous dosing of procainamide can be dangerous as its initial Vd is less than its final; thus adverse myocardial effects can often be seen as the initial ‘compartment’ and includes the cardiovascular system. Myocardial complications can initially be more pronounced. Procainamide may also have weak anticholinergic effects that produce tachycardia. Negative inotropic effects may occur in toxicity. The NAPA metabolite of procainamide lacks Nat channel blocking activity but still retains blockade of the Kt rectifier currents. It is therefore pharmacologic, similar to a type III antidysrhythmic.

Precautions

Contraindications to procainamide are similar to those for quinidine. Because of its effects on A-V nodal and His-Purkinje conduction, procainamide should be administered with caution to patients with second-degree A-V block and bundle branch block. Procainamide should not be administered to patients who have shown procaine or procainamide hypersensitivity and should be used with caution in patients with bronchial asthma. Prolonged administration should be accompanied by hematological studies, since agranulocytosis may occur.