NCIt definition : The sulfate salt form of quinidine, an alkaloid with antimalarial and antiarrhythmic
(Class la) properties. Quinidine sulfate exerts its anti-malarial activity by acting
primarily as an intra-erythrocytic schizonticide through association with the hemepolymer
(hemozoin) in the acidic food vacuole of the parasite thereby preventing further polymerization
by heme polymerase enzyme. This results in accumulation of toxic heme and death of
the parasite. Quinidine sulfate exerts its antiarrhythmic effects by depressing the
flow of sodium ions into cells during phase 0 of the cardiac action potential, thereby
slowing the impulse conduction through the atrioventricular (AV) node, reducing the
rate of phase 0 depolarization and prolonging the refractory period. Quinidine sulfate
also reduces the slope of phase 4 depolarization in Purkinje-fibres resulting in slowed
conduction and reduced automaticity in the heart.;