Laxatives and Anti-diarrhoeals

Question 1

Give the different types of laxatives

Answer 1

Bulk laxativeOsmotic laxativesFaecal softenersIrritant/stimulant laxatives

Question 2

Mechanism of bulk laxatives

Answer 2

Increase volume of non-absorbable solid residue in gut to stimulate gut distension. This stimulates peristalsis

Question 3

Give some examples of bulk laxatives

Answer 3

BranIspaghulaMethylcellulose

Question 4

ADRs of bulk laxatives

Answer 4

Gut obstructionFlatulenceAbdominal distention

Question 5

Give some examples of faecal softeners and how they would be given

Answer 5

Arachis oil - enemaGlycerol - suppository

Question 6

When would you give faecal softeners?

Answer 6

ConstipationAnal fissuresHaemmorrhoidsFaecal impaction

Question 7

Mechanism for faecal softeners

Answer 7

Loosen and soften stools

Question 8

Give some examples of osmotic laxatives

Answer 8

LactuloseSodium and magnesium saltsMovicol

Question 9

Give the routes of administration for the osmotic laxatives

Answer 9

Lactulose = oralMg & Na salts = rectalMovicol = orally with fluid as is a powder

Question 10

Mechanism for osmotic laxatives

Answer 10

Increase the water content of the bowel via osmosis

Question 11

Give the specific mechanism for lactulose

Answer 11

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.

Question 12

ADRs for osmotic laxatives

Answer 12

FlatulenceCrampsAbdominal discomfortNeed to take care to prevent intestinal obstruction

Question 13

How long does each form of osmotic laxative take to work?

Answer 13

Mg and N- work quite quickly and are quite severeLactulose = 48 hoursMovicol = 2-4 days

Question 14

Give some examples of irritant laxatives

Answer 14

SennaDanthronBisacodyl

Question 15

Mechanism of irritant laxatives

Answer 15

Increase GI peristalsis and water and electrolyte secretion by the mucosa. Potentially is due to excitation of sensory enteric nerves.

Question 16

ADRs of irritant laxatives

Answer 16

HypokalaemiaColonic atony and therefore contipation

Question 17

How can you detect abuse of irritant laxatives?

Answer 17

Melanosis cell which is pigmentation of the bowel wall.

Question 18

Give some causes of diarrhoea

Answer 18

InfectionsToxinsDrugsChronic diseaseAnxiety

Question 19

How do you treat diarrhoea generally?

Answer 19

Treat the symptoms, not the cause. Give appropriate fluid and electrolyte balance.

Question 20

What are the general classes of antidiarrhoeals?

Answer 20

Anti-motility antidiarrhoealsBulk forming antidiarrhoeals

Question 21

Examples of anti-motility antidiarrhoeals

Answer 21

Codeine - opiate analgesicImodium - opiate analogue

Question 22

Mechanism of anti-motility antidiarrhoeals

Answer 22

Act on opioid receptors in the bowel to reduce the gut motility. They also increase anal tone and reduce the sensory defecation reflex.

Question 23

ADRs of anti-motility diarrhoeals

Answer 23

NauseaVomitingAbdominal crampsConstipationDrowsiness

Question 24

When would you not give an anti-motility antidiarrhoeal?

Answer 24

With inflammatory bowel disease as it can give rise to toxic megacolon

Question 25

Give some examples of bulk-forming antidiarrhoeals

Answer 25

Isphagula

Question 26

Mechanism for bulk forming antidiarrhoeals

Answer 26

Absorb faecal fluid to increase bulk, therefore decreasing diarrhoea.

Question 27

Give the main features of irritable bowel syndrome

Answer 27

Abdominal painDiscomfortBloatingAlteration of bowel habits

Question 28

How would you treat IBS?

Answer 28

Mebeverine- affects colonic hypermobility by decreasing the spasming of intestinal muscles which is the main symptom complained about with IBS

Question 29

Describe the process of emesis

Answer 29

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.

Question 30

When is there a higher rate of aspiration of vomit?

Answer 30

Alcohol intoxicationCranial nerve lesion

Question 31

How is the process of vomiting controlled?

Answer 31

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

Question 32

Give some examples of anti-emetics

Answer 32

Dopamine receptor antagonistsSerotonin antagonistsAnti-muscarinicsHistamine antagonistsCannabinoidsBenzodiazepines

Question 33

Give some examples of D2 antagonists

Answer 33

DomperiddoneMetoclopramidePhenothiazines

Question 34

Mechanism for D2 antagonists

Answer 34

Acts on postrema and stomach to inhibits the rate of gastric emptying

Question 35

ADRs of D2 antagonists

Answer 35

Stimulates prolactin releaseMetoclopramide - extra-pyramidal side effects, so avoid in Parkinsons

Question 36

Give some examples of serotonin antagonists

Answer 36

OndansetronGranisetron

Question 37

Mechanism for serotonin antagonists

Answer 37

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.

Question 38

ADRs of serotonin antagonists

Answer 38

HeadachesConstipationFlushing

Question 39

Give a drug-drug interaction with serotonin antagonists

Answer 39

Anti-emetic effect can be enhanced by a single dose of corticosteroid

Question 40

Give some examples of anti-muscarinics

Answer 40

Hyoscine

Question 41

Mechanism for anti-muscarinics

Answer 41

Directly antagonise the muscarinic cholinergic M1 receptors which stimulate emesis

Question 42

ADRs for anti-cholinergics

Answer 42

Systemic anti-cholinergic effectsBradycardia

Question 43

Give some examples of histamine antagonists

Answer 43

Cyclizine

Question 44

Mechanism for histamine antagonists

Answer 44

Antagonise H1 receptors

Question 45

ADRs of histamine antagonists

Answer 45

Prolong QT intervalCross the BBB and have a sedative effect.