that could hinder further oxygen exchange. It was also detected that the antiarrhythmic drug procainamide interferes with pacemakers. A toxic level of procainamide leads to decrease in ventricular conduction velocity and increase of the ventricular refractory period. This results in a disturbance in the artificial membrane potential and leads to a supraventricular tachycardia which induces failure of the pacemaker and death. Thus, it prolongs QT interval of action potential and increases the risk of torsade de pointes. Procainamide could initiate leukopenia and/or agranulocytosis, which are serious hematologic disorders, and is also known for causing gastrointestinal disturbances and aggravating pre-existing abnormalities in impulse initiation and propagation. Pharmacology Mechanism of action Procainamide works as an anti-arrhythmic agent and is used to treat cardiac arrhythmia. It induces rapid block of the batrachotoxin (BTX)-activated sodium channels of the heart muscle and acts as antagonist to long-gating closures. The block is voltage-dependent and can occur from both sides; either from the intracellular or the extracellular side. Blocking from the extracellular side is weaker than from the intracellular side because it occurs via the hydrophobic pathway. Procainamide is present in charged form and probably requires a direct hydrophobic access to the binding site for blocking of the channel. Furthermore, blocking of the channel shows a decreased voltage sensitivity, which may result from the loss of voltage dependence of the blocking rate. Due to its charged and hydrophilic form, procainamide has its effect from the internal side, where it causes blockage of voltage-dependent, open channels. With increasing concentration of procainamide, the frequency of long blockage becomes less without the duration of blockage being affected. The rate of fast blocking is determined by the membrane depolarization. Membrane depolarization leads to increased blocking and decreased unblocking of the channels. Procainamide slows the conduction velocity and increases the refractory period, such that the maximal rate of depolarization is reduced. Metabolism Procainamide is metabolized via different pathways. The most common one is the acetylation of procainamide to the less-toxic N-acetylprocainamide. The rate of acetylation is genetically determined. There are two phenotypes that result from the acetylation process, namely the slow and rapid acetylator. Procainamide can also be oxidized by the cytochrome P-450 to a reactive oxide metabolite. But it seems that acetylation of the nitrogen group of procainamide decrease the amount of the chemical that would be available for the oxidative route. Other metabolites of procainamide include desethyl-N-acetylprocainamide, desethylprocainamide, p-aminobenzoic acid,