NCIt definition : An alkaloid extracted from the bark of the Cinchona tree with class 1A antiarrhythmic
and antimalarial effects. Quinidine stabilizes the neuronal membrane by binding to
and inhibiting voltage-gated sodium channels, thereby inhibiting the sodium influx
required for the initiation and conduction of impulses resulting in an increase of
the threshold for excitation and decreased depolarization during phase 0 of the action
potential. In addition, the effective refractory period (ERP), action potential duration
(APD), and ERP/APD ratios are increased, resulting in decreased conduction velocity
of nerve impulses. Quinidine exerts its antimalarial activity by acting primarily
as an intra-erythrocytic schizonticide through association with the heme polymer (hemazoin)
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.;