GENERIC NAME: quinidine
DISCONTINUED BRANDS: Quinidine Gluconate, Quinidine Sulfate
DRUG CLASS AND MECHANISM: Quinidine is an antiarrhythmic medication that is used to correct disturbances in the rhythm of the heart (antiarrhythmic). Other antiarrhythmic drugs within the same class include procainamide (for example, Pronestyl) and disopyramide (for example, Norpace). This class of antiarrhythmics is specifically called "Class I" antiarrhythmics, and they differ from other antiarrhythmic drugs because they work by interfering with the sodium channel in the membranes of cells. The sodium channel is part of the membrane (wall) surrounding every cell that allows sodium to pass through into the cell, making the cells (for example, muscle and nerve cells) excitable and, in the case of muscle cells, able to contract. Thus, the flow of sodium through these channels is necessary for the muscle cells of the heart to be stimulated to contract, and Class I antiarrhythmics decrease the electrical stimulation of the muscle cells.
There are three actions that are responsible for quinidine's ability to stop arrhythmias and prevent their recurrence. Quinidine decreases the speed of the electrical current that travels through the heart muscle that causes the heart muscle cells to contract. It also prolongs the period during which heart muscle cells can become electrically stimulated to contract and prolongs the recovery period after contraction during which the heart muscle cells cannot be stimulated to contract.
Quinidine blocks the normal effect of the vagus nerve on the heart, causing an increase in the rate at which the heart beats. Quinidine reduces the force of contraction of heart muscle cells, and therefore may impair the pumping efficiency of failing heart muscle as in congestive heart failure. Quinidine blocks alpha-receptors on the muscle cells that surround arteries which relaxes the muscle cells, lowers blood pressure ,and can cause excessively low blood pressure when combined with other drugs that also relax these muscle cells. Quinidine was approved by the FDA in July 1950.
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