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Quinidine is a class IA antiarrhythmic agent used to treat heart rhythm disturbances. It is a diastereomer of antimalarial agent quinine, originally derived from the bark of the cinchona tree. The drug causes increased action potential duration, as well as a prolonged QT interval. As of 2019, its IV formulation is no longer being manufactured for use in the United States.
It reduces the recurrence of atrial fibrillation after patients undergo cardioversion, but it has proarrhythmic effects and trials suggest that it may lead to an overall increased mortality in these patients.
Quinidine is also used to treat short QT syndrome.
Eli Lilly has discontinued manufacture of parenteral quinidine gluconate in the US, and its future availability in many countries is uncertain.
Although intravenous quinidine is sometimes used to treat Plasmodium falciparum malaria, the future availability of this agent is uncertain.
Quinidine can cause thrombocytopenia, granulomatous hepatitis, myasthenia gravis, and torsades de pointes (dangerous heart rhythm), (2025). 9780912912066, Cover Publishing Company. ISBN 9780912912066 and has been largely phased out in favor of other antiarrhythmics. Torsades can occur after the first dose. Quinidine-induced thrombocytopenia (low platelet count) is mediated by the immune system, and may lead to thrombocytic purpura.
Quinidine intoxication can lead to a collection of symptoms collectively known as cinchonism, with tinnitus (ringing in the ears) being among the most characteristic and common symptoms of this toxicity syndrome.
It seems still efficacious as an IV antimalarial against Plasmodium falciparum. This electrolyte dependent agent also increases action potentials and prolongs the QT interval. Quinidine also blocks the slowly inactivating, tetrodotoxin-sensitive sodium current, the slow inward calcium current (ICa), the rapid (IKr) and slow (IKs) components of the delayed potassium rectifier current, the inward potassium rectifier current (IKI), the ATP-sensitive potassium channel (IKATP) and Ito.
At micromolar concentrations, quinidine inhibits Na+/K+-ATPase by binding to the same receptor sites as the digitalis glycosides such as ouabain.
The effect of quinidine on the ion channels is to prolong the cardiac action potential, thereby prolonging the QT interval on the surface ECG.
Other ECG effects include a wide notched P wave, wide QRS complex, ST depression, and U wave. These are the results of both slowed depolarization and repolarization.
"Long and rebellious palpitations have ceded to this febrifuge".
"Of all the stomachic remedies, the one whose effects have appeared to me the most constant and the most prompt in many cases is quinquina Peruvian mixed with a little rhubarb."
Sénac subsequently became physician to Louis XV of France, a counselor of the state, and superintendent of the mineral waters and medicinals in France. As a result of his influence, throughout the 19th century, quinidine was used to augment digitalis therapy. It was described as das Opium des Herzens (the opium of the heart).
However, the use of quinidine to treat arrhythmia really only came into its own because a physician listened to the astute observation of one of his patients. In 1912, Karel Frederik Wenckebach saw a man with atrial fibrillation. He was a Dutch merchant, used to good order in his affairs. He would like to have good order in his heart business, also, and asked, "why there were heart specialists if they could not abolish this very disagreeable phenomenon ... he knew himself how to get rid of his attacks. As I did not believe him, he promised to come back next morning with a regular pulse, and he did."
The man had found by chance that when he took one gram of quinine during an attack, it reliably halted it in 25 minutes; otherwise it would last for two to 14 days. Wenckebach often tried quinine again, but he succeeded in only one other patient.
He made passing mention of it in his book on cardiac arrhythmias published in 1914. Four years later, Walter von Frey of Berlin reported in a leading Viennese medical journal that quinidine was the most effective of the four principal cinchona alkaloids in controlling atrial arrhythmias.
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