Quinidine, a hydantoin anticonvulsant is used alone or with phenobarbital or other anticonvulsants to treat tonic-clonic seizures, psycho-motor seizures, neuropathic pain syndromes including Diabetic neuropathy, atrial fibrillation and flutter, ventricular arrhythmias, Paroxysmal tachycardia, restoration of normal sinus rhythm, Atrial, nodal & ventricular premature beats, Ventricular fibrillation and  Malaria.

Dose of Quinidine Drugs

• Quinidine Sulfate : 200-400 mg 4-6 hours interval orally. Total dose not more than 4 gm (Tab 100 mg, 200 mg; lnj. 0.3 mg/ml). Therapeutic serum levels: 1.3-5 μg/ml Initially give test dose
• Quinidine Gluconate : 80 mg volume diluted in 5% glucose. Intravenous (IV) 25 mg/min. Total dose up to 800 mg/day.

Action of Quinidine

1. Depresses the entry of sodium into the cell during depolarisation; hence decreases diastolic depolarisation. Has negative inotropic effect by depressing the entry of calcium into cardiac muscle cells.
2. Prolongs refractory period of atria but decreases that of AV node, hence it abolishes arrhythmias due to circus movement, but increased conduction through AV node may cause sudden rise of ventricular rate.

Common side effects of Quinidine

1. Cardiac :

• Bradycardia
• Ventricular tachycardia
• Ventricular fibrillation
• P.B.
• Hypotension
• Torsades de pointes

2. Extra-Cardiac :

• Intolerance : Skin rash, fever & thrombocytopenia.
• Cinchonism : Ringing in ears, vertigo, blurred vision, tremors, Dysphoria & Deafness etc.
• Gastrointestinal Tract : Abdominal pain, Nausea, vomiting & diarrhea.
• Respiratory failure
• Cerebral : Headache & Convulsions.

Contra-indications of Quinidine

• Complete AV block,
• Severe intraventricular conduction defects,
• Left bundle-branch block, or ventricular ectopy.
• Digitalis-induced AV conduction disorders.