GI cards Flashcards
Bulk Laxatives
Examples
Ispaghula
Bran
Methylcellulose
Route of Administration
Oral
Indications
Constipation, particularly when hard stools are present
Contraindications Dysphagia Intestinal obstruction (Adhesions, ulceration) Colonic atony Faecal impaction
Mechanism of Action
Increases the volume of the non-absorbable solid residue in the gut, distending the colon and stimulating peristaltic movement.
Adverse Drug Reactions
Flatulence
Abdominal distension
GI obstruction
Therapeutic Notes
A normal fluid intake is essential
Clinical effects may take several days to develop
Faecal Softeners
Examples
Arachis Oil
Glycerol
Route of Administration
Arachis Oil – Enema
Glycerol – Suppository
Indications Constipation Faecal impaction Haemorrhoids Anal fissures
Contraindications
Children less than 3 years old
Mechanism of Action
Lubricate and soften stools
Therapeutic Notes
Safe, but not always effective
Relatively slow to take effect
Osmotic Laxatives
Examples
Lactulose
Magnesium and Sodium Salts
Movicol
Route of Administration
Lactulose – Oral
Magnesium and Sodium Salts – Rectal
Movicol – Orally with fluid (powder)
Indications
Constipation
Lactulose - Liver failure (reduced production of ammonia)
Contraindications
Intestinal obstruction
Mechanism of Action
Increase water content of the bowel via osmosis
Lactulose – Disaccharide (galactose/fructose) that cannot be hydrolysed by digestive enzymes. The fermentation of lactulose by colonic bacteria gives acetic and lactic acid. This has an osmotic effect
Adverse Drug Reactions Flatulence Cramps Abdominal discomfort Caution required to prevent intestinal obstruction
Therapeutic Notes
Magnesium and Sodium act quickly and are quite severe, so should be reserved for ‘resistant’ constipation if urgent relief is required
Lactulose takes 48 hours to work
Movicol takes 2-4 days to get relief
Irritant / Stimulant Laxatives
Examples Anthraquinone Group Senna Danthron Bisacodyl
Route of Administration
Oral
Indications
Constipation and bowel evacuation prior to medical/surgical procedures
Contraindications
Intestinal obstruction
Mechanism of Action
Increase gastrointestinal peristalsis and water and electrolyte secretion by the mucosa. Possibly by excitation of sensory enteric nerves.
Adverse Drug Reactions
Colonic atony (thus constipation)
Hypokalaemia (Changing electrolyte balance in the gut)
Therapeutic Notes
Anthraquinone group is the most frequently used.
Senna can be bought O.T.C. (Senokot)
Abuse can be detected via Melanosis Coli (pigmentation of bowel wall)
Anti-Motility Antidiarrhoeals
Examples
Codeine (opiate analgesic)
Imodium (opiate analogue)
Contraindications
Inflammatory Bowel Disease – Toxic Megacolon
Mechanism of Action Act on opioid receptors in the bowel Reduce motility (increase time for fluid reabsorption) Increase anal tone and reduce sensory defecation reflex
Adverse Drug Reactions
Nausea, vomiting, abdominal cramps, constipation drowsiness
Therapeutic Notes
Imodium is 40 times more potent than Morphine as an antidiarrhoeal agent, and penetrates the CNS poorly
Bulk Forming Antidiarrhoeals
Examples
Ispaghula
Route of Administration
Oral
Indications
Particularly useful for patients with IBS and those with ileostomy
Contraindications
Intestinal obstruction
Mechanism of Action
A relatively small amount of faecal fluid (10-20ml) influences composition. Bulk forming antidiarrhoeals absorb this fluid.
Dopamine (D2) Receptor Antagonists (Anti Emetics)
Examples
Domperidone
Metoclopramide
Phenothiazines
Route of Administration
Oral
Rectal (extensive 1st pass metabolism)
Indications
Acute nausea/vomiting
Especially induced by L-DOPA or dopamine agonists
Mechanism of Action
Acts on the Postrema on the floor of the 4th ventricle
Acts on the stomach to increase the rate of gastric emptying
Adverse Drug Reactions
Stimulates prolactin release
Metoclopramide – extra-pyramidal reactions (dystonia) occur in 1%, therefore is avoided in Parkinson’s disease
Examples
Domperidone
Metoclopramide
Phenothiazines
Route of Administration
Oral
Rectal (extensive 1st pass metabolism)
Indications
Acute nausea/vomiting
Especially induced by L-DOPA or dopamine agonists
Mechanism of Action
Acts on the Postrema on the floor of the 4th ventricle
Acts on the stomach to increase the rate of gastric emptying
Adverse Drug Reactions
Stimulates prolactin release
Metoclopramide – extra-pyramidal reactions (dystonia) occur in 1%, therefore is avoided in Parkinson’s disease
Examples
Ondansetron
Granisetron
Route of Administration
Oral, IV or IM
Indications
In high doses in radiation sickness, chemotherapy sickness, post operatively
Mechanism of Action
5-HT is released into the gut, reducing Vagus activity, therefore effective at deactivating the vomiting centre (the Postrema on the floor of the 4th ventricle)
Blocks Serotonin receptors in Chemoreceptor Trigger Zone
Adverse Drug Reactions
Headaches, constipation, flushing
Drug-Drug Interactions
Anti-Emetic effect can be enhanced by a single dose of a corticosteroid
Anti-Muscarinics (Anti Emetic)
Examples
Hyoscine
Route of Administration
Oral or patch
Indications
Motion sickness
Mechanism of Action
Direct antagonist of muscarinic cholinergic receptors (M1)
Adverse Drug Reactions
Systemic anti-cholinergic effects, bradycardia
Histamine H1 Receptor Antagonists (Anti Emetic)
Examples
Cyclizine
Route of Administration
Oral, IV or IM
Indications
Acute nausea and vomiting
Contraindications
Myocardial ischaemia
Mechanism of Action
Antagonises H1 receptors
Adverse Drug Reactions
Can cause QT prolongation
Crosses the BBB – Sedative effect
