Quinidine is a medication used to restore normal sinus rhythm, treat atrial fibrillation and flutter, and treat ventricular arrhythmias. It can be found under the brand name Nuedexta. Quinidine is a D-isomer of quinine present in the bark of the Cinchona tree and similar plant species. This alkaloid was first described in 1848 and has a long history as an antiarrhythmic medication. Quinidine is considered the first antiarrhythmic drug (class Ia) and is moderately efficacious in the acute conversion of atrial fibrillation to normal sinus rhythm. It prolongs cellular action potential by blocking sodium and potassium currents. A phenomenon known as “quinidine syncope” was first described in the 1950s, characterized by syncopal attacks and ventricular fibrillation in patients treated with this drug. Quinidine has a complex electrophysiological profile that has not been fully elucidated. The antiarrhythmic actions of this drug are mediated through effects on sodium channels in Purkinje fibers. Quinidine blocks the rapid sodium channel (INa), decreasing the phase zero of rapid depolarization of the action potential. Quinidine also reduces repolarizing K+ currents (IKr, IKs), the inward rectifier potassium current (IK1), and the transient outward potassium current Ito, as well as the L-type calcium current ICa and the late INa inward current. The type 5 subunit alpha channel is targeted. The reduction of these currents leads to the prolongation of the action potential duration. By shortening the plateau but prolonging late depolarization, quinidine facilitates the formation of early afterdepolarisation (EAD). Some side effects of using quinidine may include nausea, heartburn, fever, and dizziness. Quinidine is administered as an oral tablet.

Quinidine Pathway (New) References