Quinidine

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Quinidine
Systematic (IUPAC) name
2-ethenyl-4-azabicyclo[2.2.2]oct-5-yl)- (6-methoxyquinolin-4-yl)-methanol
Identifiers
CAS number	56-54-2
ATC code	C01BA01
PubChem	5953
DrugBank	APRD00136
Chemical data
Formula	C20H24N2O2
Mol. weight	324.417 g/mol
Pharmacokinetic data
Bioavailability	70-80%
Metabolism	50-90% Hepatic
Half life	6-8h
Excretion	Renal
Therapeutic considerations
Pregnancy cat.	?
Legal status
Routes	Oral

Quinidine is a pharmaceutical agent that acts as a class I antiarrhythmic agent in the heart. It is a stereoisomer of quinine, originally derived from the bark of the cinchona tree.

Chemically it is known as (2-ethenyl-4-azabicyclo[2.2.2]oct-5-yl)- (6-methoxyquinolin-4-yl)-methanol

OR

6'-mehoxycinchonan-9-ol

OR

6' methoxy-alpha (5-vinyl-2-quinuclidinyl)-4-quinoline methanol.

Like all other class I antiarrhythmic agents, quinidine primarily works by blocking the fast inward sodium current (I_Na). Quinidine's effect on I_Na is known as a use dependent block. This means that at higher heart rates, the block increases, while at lower heart rates the block decreases. The effect of blocking the fast inward sodium current causes the phase 0 depolarization of the cardiac action potential to decrease (decreased V_max).

Quinidine also blocks the slowly inactivating tetrodotoxin-sensitive Na current, the slow inward calcium current (I_Ca), the rapid (I_Kr) and slow (I_Ks) components of the delayed potassium rectifier current, the inward potassium rectifier current (I_KI), the ATP-sensitive potassium channel (I_KATP) and I_to.

The effect of quinidine on the ion channels is to prolong the cardiac action potential, thereby prolonging the QT interval on the surface EKG.

The half life of oral quinidine is 6 to 8 hours, and it is eliminated by the cytochrome P450 system in the liver. About 20 percent is excreted unchanged via the kidneys. Quinidine is also an inhibitor of the cytochrome P450 enzyme 2D6, and can lead to increased blood levels of lidocaine, Beta blockers, opioids, and some anti-depressants.

Intravenous quinidine is also indicated for treatment of P. falciparum malaria.

Quinidine-induced thrombocytopenia (low platelet count) is mediated by the immune system, and may lead to thrombocytic purpura.

Quinidine intoxication can lead to a collection of symptoms collectively known as cinchonism with tinnitus (ringing in the ears) being among the most characteristic and common symptoms of this toxicity syndrome.

[edit] References

• MedlinePlus
• Poisons Information Monograph

[edit] See also

• Antiarrhythmic agents
• Cardiac action potential

Antiarrhythmic agents (C01B)edit
class Ia:	Ajmaline, Disopyramide, Prajmaline, Procainamide, Quinidine, Sparteine
class Ib:	Aprindine, Lidocaine, Mexiletine, Tocainide
class Ic:	Encainide, Flecainide, Lorcainide, Moricizine, Propafenone
class II:	Propranolol, Metoprolol, Nadolol, Atenolol, Acebutolol, Pindolol, Sotalol see Beta blockers (C07)
class III:	Amiodarone, Bretylium tosilate, Bunaftine, Dofetilide, Ibutilide
class IV:	Verapamil, Diltiazem see Calcium channel blockers (C08)
class V:	Adenosine, Atropine, Digoxin