Gastrointestinal system and nutrition Flashcards
When is loperamide used?
Antimotolity drug used as symptomatic treatment for diarrhoea, usually in the context of irritable bowel syndrome or viral gastroenteritis.
How does loperamide work?
Loperamide is pharmacologically similar to pethidine. However, unlike pethidine, it does not penetrate the central nervous system so has no analgesic effects.
It is an agonist of the mu-opioid receptors in the gastrointestinal tract.
This increases non-propulsive contractions of the gut smooth muscle but reduces propulsive (peristaltic) contractions. As a result, transit of bowel contents is slowed and anal sphincter tone is increased. Slower gut transit also allows more time for water absorption, which in the context of water diarrhoea) has a desirable effect in hardening the stool. Other opioids (e.g. codeine phosphate) have similar effects but less reason to use them.
What are the important adverse effects of loperamide?
Loperamide is a safe drug with few adverse effects, these are mostly GI, predictable from its mech of action: constipation, abdominal cramping and flatulence.
In whom should loperamide be avoided?
In acute ulcerative colitis where inhibition of peristalsis may increase the risk of megacolon and perforation.
Also if there is a possibility of C.diff colitis, particularly if in patients who develop diarrhoea in association with broad spectrum antibiotics.
What are the interactions of loperamide?
None of clinical significance
Can loperamide syrup be purchased OTC?
Nope. POM only.
Why would a hospital patient who develops diarrhoea not be prescribed loperamide immediately?
Due to the risk of inhibiting peristalsis in C.diff colitis, should wait until there is a better idea of the aetiology of the condition such as a positive viral PCR and/or negative c.diff toxin test.
Antimuscarinics such as _____ ___________ are first line treatment for what syndrome?
Hyoscine butylbromide and IBS, they are used for their antispasmodic effect.
What is the mechanism of action of antimuscarinics in IBS?
Antimuscarinic drugs bind to the muscarinic receptor, where they act as a competitive inhibitor of acetylcholine. Stimulation of the muscarinic receptor brings about a wide range of parasympathetic ‘rest and digest’ effects, by blocking these receptors they cause increased heart rate and conduction, reduced smooth muscle tone and peristaltic contraction.
In whom should antimuscarinics be used with caution?
Patients susceptible to angle-closure glaucoma, in whom they can precipitate a dangerous rise in intraocular pressure.
Also generally be avoided in patients at risk of arrhythmias (eg those with significant cardiac disease) unless the indication for use is bradycardia.
What type of antidepressant drug can lead to more pronouced side effects of antimuscarinic drugs such as atropine, hyoscine butylbromide and glycopyrronium?
TCAs such as amitriptyline.
What are metoclopramide and domperidone?
Dopamine D2-receptor antagonists, antiemetics.
What is the mechanism of action of metoclopramide and domperidone?
The D2 receptor is the main receptor in the chemoreceptor trigger zone (CTZ) which is the area responsible for sensing emetogenic substances in the blood (e.g. drugs).
Also dopamine is an important neurotransmitter in the gut, where it promotes relaxation of the stomach and lower oesophageal sphincter and inhibits gastroduodenal coordination.
Drugs that block D2 receptors therefore have a prokinetic effect - promoting gastric emptying - which contributes to their antiemetic action.
Why is domperidone often preffered to metoclopramide?
Domperidone does not cross the blood brain barrier thus does not cause extrapyramidal side effects. The chemoreceptor trigger zone is largely outside the blood-brain barrier.
Metoclopramide can cause extrapyramidal side effects via the same mechanisms as what other type of drugs?
Anti-pscyhotic
