Laxatives and Anti-diarrhoeals Flashcards
Give the different types of laxatives
Bulk laxativeOsmotic laxativesFaecal softenersIrritant/stimulant laxatives
Mechanism of bulk laxatives
Increase volume of non-absorbable solid residue in gut to stimulate gut distension. This stimulates peristalsis
Give some examples of bulk laxatives
BranIspaghulaMethylcellulose
ADRs of bulk laxatives
Gut obstructionFlatulenceAbdominal distention
Give some examples of faecal softeners and how they would be given
Arachis oil - enemaGlycerol - suppository
When would you give faecal softeners?
ConstipationAnal fissuresHaemmorrhoidsFaecal impaction
Mechanism for faecal softeners
Loosen and soften stools
Give some examples of osmotic laxatives
LactuloseSodium and magnesium saltsMovicol
Give the routes of administration for the osmotic laxatives
Lactulose = oralMg & Na salts = rectalMovicol = orally with fluid as is a powder
Mechanism for osmotic laxatives
Increase the water content of the bowel via osmosis
Give the specific mechanism for lactulose
Lactulose is a disaccharide that cannot be hydrolysed by digestive enzymes. The fermentation of lactulose by colonic bacteria gives rise to acetic and lactic acid which have an osmotic effect.
ADRs for osmotic laxatives
FlatulenceCrampsAbdominal discomfortNeed to take care to prevent intestinal obstruction
How long does each form of osmotic laxative take to work?
Mg and N- work quite quickly and are quite severeLactulose = 48 hoursMovicol = 2-4 days
Give some examples of irritant laxatives
SennaDanthronBisacodyl
Mechanism of irritant laxatives
Increase GI peristalsis and water and electrolyte secretion by the mucosa. Potentially is due to excitation of sensory enteric nerves.
ADRs of irritant laxatives
HypokalaemiaColonic atony and therefore contipation
How can you detect abuse of irritant laxatives?
Melanosis cell which is pigmentation of the bowel wall.
Give some causes of diarrhoea
InfectionsToxinsDrugsChronic diseaseAnxiety
How do you treat diarrhoea generally?
Treat the symptoms, not the cause. Give appropriate fluid and electrolyte balance.
What are the general classes of antidiarrhoeals?
Anti-motility antidiarrhoealsBulk forming antidiarrhoeals
Examples of anti-motility antidiarrhoeals
Codeine - opiate analgesicImodium - opiate analogue
Mechanism of anti-motility antidiarrhoeals
Act on opioid receptors in the bowel to reduce the gut motility. They also increase anal tone and reduce the sensory defecation reflex.
ADRs of anti-motility diarrhoeals
NauseaVomitingAbdominal crampsConstipationDrowsiness
When would you not give an anti-motility antidiarrhoeal?
With inflammatory bowel disease as it can give rise to toxic megacolon
Give some examples of bulk-forming antidiarrhoeals
Isphagula
Mechanism for bulk forming antidiarrhoeals
Absorb faecal fluid to increase bulk, therefore decreasing diarrhoea.
Give the main features of irritable bowel syndrome
Abdominal painDiscomfortBloatingAlteration of bowel habits
How would you treat IBS?
Mebeverine- affects colonic hypermobility by decreasing the spasming of intestinal muscles which is the main symptom complained about with IBS
Describe the process of emesis
Pyloric sphincter closes, cardia and oesophagus relax. Gastric contents are propelled by contraction of the abdominal wall and diaphragm. Glottis closes, soft palate elevates to prevent aspiration of vomit.
When is there a higher rate of aspiration of vomit?
Alcohol intoxicationCranial nerve lesion
How is the process of vomiting controlled?
Stimulation of the Postrema, which is found on the floor of the 4th ventricle. This is where the vomiting centre is found. It detects toxins in the blood and then stimulates vomiting. ORStimulation of the vestibular apparatus (motion sickness) which goes on to stimulate the medullry centre
Give some examples of anti-emetics
Dopamine receptor antagonistsSerotonin antagonistsAnti-muscarinicsHistamine antagonistsCannabinoidsBenzodiazepines
Give some examples of D2 antagonists
DomperiddoneMetoclopramidePhenothiazines
Mechanism for D2 antagonists
Acts on postrema and stomach to inhibits the rate of gastric emptying
ADRs of D2 antagonists
Stimulates prolactin releaseMetoclopramide - extra-pyramidal side effects, so avoid in Parkinsons
Give some examples of serotonin antagonists
OndansetronGranisetron
Mechanism for serotonin antagonists
Reduces release of 5HT from the guts, as it acts on the vagus nerve. This helps to deactivate the postrema. Also blocks serotonin receptors in the chemoreceptor trigger zone.
ADRs of serotonin antagonists
HeadachesConstipationFlushing
Give a drug-drug interaction with serotonin antagonists
Anti-emetic effect can be enhanced by a single dose of corticosteroid
Give some examples of anti-muscarinics
Hyoscine
Mechanism for anti-muscarinics
Directly antagonise the muscarinic cholinergic M1 receptors which stimulate emesis
ADRs for anti-cholinergics
Systemic anti-cholinergic effectsBradycardia
Give some examples of histamine antagonists
Cyclizine
Mechanism for histamine antagonists
Antagonise H1 receptors
ADRs of histamine antagonists
Prolong QT intervalCross the BBB and have a sedative effect.
