Quinidine

• Class IA prototype antiarrhythmic.
• Dextroisomer of quinine.
• Antimalerial and anti pyretic action.

Pharmacological structure

Obtained from Cinchana Plant.

Twobasic Nitrogens.

pK-10.

Reduces Na ion  current by binding to open Na ion  channels resulting in depression of automaticity of ectopic foci.

Available as sulphate ,gluconate.

Quinidine sulphate is oral  prepn  commonly,can be available as IM.

Na channel blockers or fast channel blockers.

 

Primary indication of quinidine

Acute and Chronic supraventricular dyrhythmias, Atrial fibrillation or atrial flutter.,premature ventricular contractions ,Wolf-Parkinsons –White syndrome.

First administer digitalis prior to administration of quinidine to avoid paradoxical increase in rate of ventricular response.

 

Dosages: 200-400 mg QID.

Peak plasma level attends in 60-90 min.

Elimination half time-5-12 hrs.

Therapeutic blood levels-1.2 -4 micro gram /ml.

IM- painful.

IV- hypotension because of alpha receptor blockade,peripheral vasodilatation and myocardial depression.

Mechanism

1. Decrease slope of phase 4 depolarisation.
2. Decreased enhanced automaticity and suppresses cardiac dysrhythmias.
3. Increases fibrillation threshold in atria and ventricles.
4. Slowing of conduction of cardiac impulses thru normal and abnormal fibers.
5. Abolish reentry dysarhthmias by prolonging conduction of cardiac impulse in injured area.
6. Reflex increase sinus rate secondary to vasodilatation ,anticholinergic effect.
7. High concentration infranodal conduction is slowed and blocked,bundle branch block,complete AV block ,asystole .QT interval is prolonged.
8. Administration of quinidine increase digoxin by releasing glycoside from protein binding site.

 

Metabolism

70-80 % protiene bound in plasma mainly with HB.

Hepatic excretion 20 % renal.if urine is alkaline excretion  decreases up to 50 %.

 

Side-effects

1. Low therapeutic ratio.

Serious side effect is quinidine syncope [various conduction  block,asystole ,Qt interval prolongation.

2. Prolonging P-R  interval .QRS ,QT interval.Torsades de ponites AV block and heart failure.

 

Always monitor  ECG,baseline QT interval while admistering quinidine.

 

DOSE SHOULD NOT BE MORE THAN 4 GM /DAY ORAL.

 

NONCARDIAC EFFECTS

1. CNS- Vertigo,confusion ,light headedness,depression ,dementia.
2. Respiratory – asthmatic attack.
3. GI- Nausea ,vomiting ,pain, hepatotoxicity.
4. Haemolytic anaemia- fever,agranulocytosis, thrombocytopenia.
5. photosensitivity.                                                                                              dr.ajita