Procainamide is a drug belonging to the group of antiarrhythmic drugs. The substance is used primarily in the therapy of cardiac arrhythmias.
What is procainamide?
Procainamide is a class Ia antiarrhythmic drug. These worsen the excitability of heart cells, leading to prolongation of the action potential. As a result, the heart cells are not as excitable and superfluous cardiac activity ceases. Class I antiarrhythmics correspond to the group of sodium channel blockers. However, procainamide is not a first-line agent, but is used almost exclusively as a reserve antiarrhythmic agent in Europe. The bioavailability of procainamide is 80 percent; only 20 percent of the active substance is bound to the so-called plasma proteins in the blood. The drug is metabolized predominantly in the liver by the hepatic cytochrome P450 system. The plasma half-life is on average three hours. This means that within this period, the concentration of procainamide in blood plasma drops to half of the original value. Procainamide is excreted by the kidneys.
Pharmacologic action
Procainamide belongs to the class of sodium channel blockers. These are also called sodium channel antagonists. They bind to a voltage-gated sodium channel that is responsible for depolarization in the action potential. The action potential is a transient deviation of the membrane potential of a cell into the positive range. Without sufficient depolarization, no action potential and thus no stimulus transmission in the area of the nerve fibers and the cells is possible. The sodium channel blockers are divided into different subclasses according to their affinity for the channel and their speed of action. Procainamide belongs to class Ia. These block sodium channels and slow the rate of depolarization. By inhibiting potassium channels, procainamide also causes a prolongation of the repolarization time and, in summary, leads to a prolongation of the action potential.
Medical application and use
The antiarrhythmic drug was developed for the therapy of cardiac arrhythmias. For example, refractory ventricular and supraventricular tachycardias are among the indications for treatment with procainamide. Ventricular arrhythmias originate in the conduction system of the heart near the so-called His bundle, a part of the conduction system. In ventricular tachycardia, the heart beats up to 320 times per minute. This is also referred to as ventricular fibrillation. Supraventricular tachycardias, on the other hand, occur above the ventricles, in the area of the sinus node or the atria. Procainamide is also used for tachyarrhythmias. A tachyarrhythmia is a combination of a heart rhythm disturbance (arrhythmia) and tachycardia, or a heartbeat that is too fast.
Risks and side effects
Common side effects of procainamide include circulatory disturbances and low blood pressure (hypotension). Fever may also occur when taking the antiarrhythmic drug. In rarer cases, so-called agranulocytosis can develop. This results in a complete deficiency of certain white blood cells, the granulocytes, in the blood. Patients suffer from a pronounced feeling of illness, bacterial infections with chills and fever, and mucosal necrosis of the anus, genitals, and throat. Via induction of antinuclear antibodies, procainamide can provoke systemic lupus erythematosus. This is a systemic disease with symptoms such as fever, muscle inflammation, prominent redness of the cheeks and nose, renal changes, neurologic symptoms, or marked changes in blood counts. Side effects that may also occur while taking procainamide include dry mouth, disturbances in taste sensation, headache, and dizziness. Nausea, vomiting, and constipation are also potential adverse drug reactions. Procainamide should not be used in cases of known hypersensitivity. Contraindications include heart failure as well as a slowed heartbeat. Similarly, procainamide is not suitable for patients with disorders of the cardiac conduction system, such as sick sinus syndrome.Within the first three months, use of procainamide is contraindicated, as are low blood pressure, electrolyte imbalances and severe bronchial asthma. The autoimmune disorder myasthenia gravis, which is associated with muscle paralysis, is also among the contraindications. In addition, procainamide should not be taken during pregnancy or while breastfeeding.