Quinidine

Quinidine is a medication that acts as a class I antiarrhythmic agent (Ia) in the heart. It is a stereoisomer of quinine, originally derived from the bark of the cinchona tree. The drug causes increased action potential duration, as well as a prolonged QT interval.'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 mixed with a little rhubarb.' Quinidine is a medication that acts as a class I antiarrhythmic agent (Ia) in the heart. It is a stereoisomer of 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 it is no longer available in the United States. Quinidine is occasionally used as a class I antiarrhythmic agent to prevent ventricular arrhythmias, particularly in Brugada Syndrome, although its safety in this indication is uncertain. Quinidine increases the likelihood of maintaining sinus rhythm after conversion from atrial fibrillation, but has pro‐arrhythmic effects and may increase mortality. It 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. According to a recent meta-analysis, there is only one small study that has shown that a combination of dextromethorphan and quinidine alleviates symptoms of easy laughing and crying (pseudobulbar affect) in patients with amyotrophic lateral sclerosis and multiple sclerosis. Although intravenous quinidine is sometimes used to treat Plasmodium falciparum malaria, its US manufacturer, Eli Lilly, no longer manufactures quinidine and the future availability of this agent in the US and other countries is uncertain. Quinidine is also an inhibitor of the cytochrome P450 enzyme 2D6, and can lead to increased blood levels of lidocaine, beta blockers, opioids, and some antidepressants. Quinidine also inhibits the transport protein P-glycoprotein and so can cause some peripherally acting drugs such as loperamide to have central nervous system side effects, such as respiratory depression, if the two drugs are coadministered.