Metoclopramide (Reglan) stimulates upper GI tract motility and has both central and peripheral actions. Centrally, it is a dopamine antagonist, an action that is important both for its often desirable antiemetic effect and other less desirable effects. Peripherally, it stimulates the release of intrinsic postganglionic stores of acetylcholine and sensitizes the gastric smooth muscle to muscarinic stimulation. The ability of metoclo-pramide to antagonize the inhibitory neurotransmitter effect of dopamine on the GI tract results in increased gastric contraction and enhanced gastric emptying and small bowel transit.
Metoclopramide is rapidly absorbed following an oral dose in a patient with intact gastric emptying. Peak plasma concentration is achieved within 40 to 120 minutes. With normal renal function, plasma half-life is about 4 hours. About 20% of an oral dose is eliminated unchanged in the urine, while 60% is eliminated as sulfate or glucuronide conjugates.
Improved gastric emptying will frequently alleviate symptoms in patients with diabetic, postoperative, or id-iopathic gastroparesis. Since metoclopramide also can decrease the acid reflux into the esophagus that results from slowed gastric emptying or lower esophageal sphincter pressure, the drug can be used as an adjunct in the treatment of reflux esophagitis.
Side effects include fatigue, insomnia, and altered motor coordination. Parkinsonian side effects and acute dys-tonic reactions also have been reported. Metoclopramide stimulates prolactin secretion, which can cause galactor-rhea and menstrual disorders. Extrapyramidal side effects seen following administration of the phenothiazines, thioxanthenes, and butyrophenones may be accentuated by metoclopramide.
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