Health Centres - Maxolon injection (metoclopramide)
How does it work?
Maxolon injection contains the active ingredient metoclopramide hydrochloride, which is a type of medicine called a dopamine antagonist. (NB. Metoclopramide is also available without a brand name, ie as the generic medicine.) Metoclopramide is an antisickness medicine, though it also has other uses due to its action on the gut.
Metoclopramide works primarily by blocking dopamine receptors found in an area of the brain known as the chemoreceptor trigger zone (CTZ). The CTZ is activated by nerve messages from the stomach when an irritant is present. It is also activated directly by agents circulating in the blood, for example anti-cancer medicines. Once activated, it sends messages to another area of the brain, the vomiting centre, which in turn sends messages to the gut, causing the vomiting reflex.
Blocking the dopamine receptors in the CTZ prevents nausea messages from being sent to the vomiting centre. This reduces the sensation of sickness and prevents vomiting.
Metoclopramide also acts in the upper end of the digestive system, where it enhances the action of a natural chemical called acetylcholine. Increasing the action of acetylcholine results in the tightening of the muscles at the entry to the stomach, relaxation of the muscles at the exit of the stomach and increased contraction of the muscles in the stomach itself. These actions speed the passage of food through the stomach into the intestine, which physically helps to prevent vomiting.
Both actions make metoclopramide useful in treating nausea and vomiting due to many causes, including anti-cancer chemotherapy and radiotherapy, various digestive disorders, heart failure, following surgery and anaesthetics, and in migraine.
Due to its action on the gut, metoclopramide also has several other uses. It is useful in migraine, not only for relieving nausea, but also because during a migraine attack stomach emptying is slowed, which can prevent painkillers taken by mouth from being absorbed. Metoclopramide speeds up the passage of painkillers from the stomach to the intestine, from where they are absorbed to relieve the headache.
Metoclopramide is often given before investigative procedures in hospital for its action on the gut, for example it helps to speed the passage of a barium meal through the gut.
Metoclopramide can also be used to restore normal muscle tone and function to the gut following surgery and in various digestive disorders. This helps relieve symptoms such as indigestion, pain, bile regurgitation, flatulence, acid reflux and heartburn.
Maxolon injection may be administered into a muscle (intramuscularly) or vein (intravenously).
What is it used for?
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