Atrial Fibrillation: Quinidine

• Although classified as a sodium channel blocker, quinidine also blocks K+ channels.

  • Most antiarrhythmic agents have such multiple actions.

• Sodium channel blockade results in

  • an increased threshold

  • decreased automaticity.

• Potassium channel blockade results in action potential (AP) prolongation (width increases).

• Quinidine gluconate-Clinical Use:

  • Maintains normal sinus rhythm in patients who have experienced atrial flutter or fibrillation.

  • Prevents ventricular tachycardia or fibrillation.

• Quinidine gluconate (Quinaglute, Quinalan) administration results in vagal inhibition (anti-muscarinic) and alpha-adrenergic receptor blockade.

• Adverse effects include cinchonism (headaches and tinnitus), diarrhea.

• Quinidine is also associated with torsades de pointes, a ventricular arrhythmias associated with marked QT prolongation.

  • This potentially serious arrhythmia occurs in 2% - 8% if patients, even if they have a therapeutic or subtherapeutic quinidine blood level.

Category: Pharmacology Notes