Metoclopramide, Gastric Emptying and L-Dopa Absorption

Abstract

Summary: The role of gastric emptying in the bioavailability of L-dopa has been investigated using metoclopramide pre-treatment to stimulate gastric and intestinal motility. Plasma level profiles of dopa were determined in 12 healthy subjects and in one patient with Parkinson's disease. Three effects of metoclopramide on L-dopa absorption were observed. The rate of absorption was increased, irregular absorption was almost completely eliminated and the overall absorption of unchanged drug was increased. Similar effects were seen in the normal subjects and in a patient on chronic treatment. The effects of metoclopramide were most likely due to the rapid delivery of ingested L-dopa from the stomach into the small intestine. It is suggested that absorption of the drug from the small intestine is rapid because of the presence of an active transport mechanism. Further, the increased overall absorption of the drug after metoclopramide suggested that ‘first pass’ metabolism of L-dopa was more readily saturable than its intestinal transport system.