Quinine is a derivate of the bark of the South American cinchona tree. Quinidine is a stereoisomer of quinine; it is a "class 1a antiarrhythmic drug" and also an antimalarial agent.
As an "Antiarrhythmic":
Note: The use of quinidine for the above indications has mostly been replaced by better pharmacological therapies such as amiodarone and procainamide.
Plasmodium Falciparum Malaria: Quinidine gluconate is acknowledged as an effective treatment of severe and complicated Malaria both alone as a therapy or in combination with exchange transfusion. EKG monitoring for prolongation of QT interval and QRS changes along with CBC, liver and renal function testing should be done on a routine basis when giving quinidine as an IV infusion or for a prolonged period.
Antiarrhythmic: Class 1a antiarrhythmic agents (example - quinidine, procainamide, disopyramide, ajmaline) work by inhibiting the fast inward sodium current, depressing the phase 0 of the action potential hence dampening the excitability of cardiac muscles which in turn prolongs the action potential and decreases automaticity. Quinidine's effect on fast inward sodium current is known as a 'use-dependent block' - this means at higher heart rates, the block increases, while at lower heart rates, the block decreases. Quinidine has also been shown to decrease potassium efflux during repolarization, inhibition of slow delayed rectifier potassium current, and shows a "reverse use dependence" pattern (less current suppression at more frequent depolarizations) and calcium transport across cell membranes.
Antimalarial: It works as an antimalarial agent by having activity against the erythrocytic stage of the Plasmodium species, and it acts by building up in the parasites food vacuole, it forms a complex with heme which prevents the crystallization in the parasites food vacuole. Cytotoxic-free heme accumulates secondary to inhibited heme polymerase activity.
Quinidine also has anticholinergic activity.
Quinidine is available as both parenteral and oral preparations.
Pharmacodynamics and Pharmacokinetics:
Quinidine is well known for its toxicity, causing QT prolongation and, in severe cases, a pleomorphic arrhythmia, a.k.a. "Torsades de pointes." This condition can be fatal, and the management of the situation includes discontinuation of the drug, institution of cardiac and electrolyte (potassium and magnesium) monitoring, management of hypoxia. Prompt management of torsades de pointes can be done by giving magnesium sulfate and terminating prolonged episodes by electrical cardioversion, in refractory cases isoproterenol or transvenous pacing is an option.
Quinidine is one of the oldest drugs known for the management of arrhythmias, and still has utility in the management of early repolarization syndrome, Brugada syndrome and idiopathic ventricular fibrillation, and certain infections such as Plasmodium falciparum malaria. A team approach is necessary amongst physicians, nurses, cardiologist, rheumatologist, a pharmacist for early detection and management of the drug toxicity which can be fatal at times (cardiology - as an antiarrhythmic/proarrhythmic, rheumatologist - known to cause lupus-like syndrome, infectious disease specialist - used in severe malaria), nurses for adverse effect monitoring and proper drug administration, pharmacists for correct drug dosing. The choice of the patient for the treatment is also essential for deciding therapy with quinidine, such as dose adjustment may be required in neonates, elderly, patients with CHF, hepatic or renal dysfunction and patients who are on other drugs such as digoxin and the ones known to prolong the QT interval. While inpatient consults with the cardiologist and intensivist about ICU care and monitoring while in the hospital are indicated. As all these interactions and responsibilities demonstrate, an interprofessional healthcare team approach is necessary for effective and safe therapy with quinidine. [Level 5]
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