ABSTRACT
Metoclopramide, a synthetic substituted benzamide, is a dopamine receptor antagonist, an antiemetic, and a stimulant of upper gastrointestinal (GI) motility. The drug is a derivative of p-aminobenzoic acid and is structurally related to procainamide and dibucaine, but lacks local anesthesic and antiarrhythmic properties. In this chapter, a new inhibitor of serum cholinesterase activity is described. Metoclopramide has been found to produce a reversible and competitive-type inhibition of the enzyme with respect to substrate. This finding suggests a new approach to explain the mechanism of action of the drug. Metoclopramide is considered a potent dopamine-receptor antagonist; some of the actions of this drug on GI smooth muscle may be mediated via antagonism of dopaminergic neurotransmission, but since cholinergic mechanism is responsible for most excitatory motor activity in the GI tract, it suggests that the therapeutic effects of metoclopramide are principally caused by cholinergic-like activity of drug.
