Everything about Quinidine totally explained
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.
Mechanism
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 ECG.
Elimination
The half life of oral quinidine is 6 to 8 hours, and it's eliminated by the
cytochrome P450 system in the liver. About 20% is excreted unchanged via the kidneys.
Side effects and other uses
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.
Quinidine also inhibits the transport protein
P-glycoprotein and so can cause some peripherally acting drugs such as
loperamide to have CNS side effects such as respiratory depression if the two drugs are co-administered.
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.
Quinidine-based ligands are used in AD-mix-β for
Sharpless asymmetric dihydroxylation.
Further Information
Get more info on 'Quinidine'.
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