Constipation: Laxatives Flashcards
what is constipation?
Defaecation that is unsatisfactory because of:
1) Infrequent stools
3) Difficult stool passage
3) Seemingly incomplete defaecation
who does constipation occur most commonly in? (3)
It can occur at any age and is commonly seen in:
1) Women
2) Elderly
3) Pregnancy
New onset constipation, especially in patients over 50 years of age should be investigated due to risk of malignancy. which other symptoms should prompt urgent investigation? (4)
1) Anaemia
2) Abdominal pain
3) Weight loss
4) Blood in the stool
Outline the diet and lifestyle advice given to those with constipation.
1) Increase dietary fibre, fluid intake and exercise
2) whole grains, fruits and vegetables: increased gradually to reduce bloating and flatulance. Effects may be seen in a few days but it can take as long as 4 weeks
3) Fruits and juices high in fibre and sorbitol, can help prevent and treat constipation
Laxative abuse may lead to which electrolyte disturbance
Hypokalaemia
List 4 classes of laxatives (4)
1) Bulk-forming laxatives
2) Stimulant laxatives
3) Faecal softeners
4) Osmotic laxatives
What conditions are osmotic laxatives such as lactulose, macrogol and phosphate enemas indicated for? (3)
1) Constipation and faecal impaction.
2) Bowel preparation prior to surgery or endoscopy.
3) Hepatic encephalopathy (lactulose)
Outline the MoA of osmotic laxatives
Increase the amount of water in the large bowel, either by drawing fluid from the body into the bowel or by retaining the fluid they were administered with. This stimulating peristalsis.
why is lactulose useful in the treatment of hepatic encephalopathy?
It produces an osmotic diarrhoea of low faecal pH, and discourages the proliferation of ammonia-producing organisms
1) list the Important adverse effects of osmotic laxatives
2) why should phosphate enemas be used with caution?
3) Osmotic laxatives can sometimes cause dehydration. which osmotic laxative is least likely to do this?
1) Flatulence, abdominal cramps and nausea common
2) Phosphate enemas can cause local irritation and electrolyte disturbances
3) Macrogols- may reduce the dehydrating effect sometimes seen with osmotic laxatives.
which patient are osmotic laxatives contraindicated in?
1) Intestinal obstruction as there is a risk of perforation. 2) Phosphate enemas can cause significant fluid shifts, so should be used with caution in heart failure, ascites and when electrolyte disturbances are present.
What adverse drug interactions can occur with osmotic laxatives?
no significant adverse drug interactions but the effects of warfarin may be slightly increased
state the dose of lactulose in an adult for the following:
1) Constipation
2) Hepatic encephalopathy
1) Initially 15 mL twice daily, adjusted according to response.
2) 30–50 mL TDS, subsequently adjusted to produce 2–3 soft stools per day.
How long does it take for lactulose to work and who should it be used in caution with?
1) up to 48 hours to act
2) lactose intolerance, intestinal obstruction
list 4 stimulant laxatives
1) Senna (also co-danthramer and co-danthrusate)
2) Bisacodyl
3) Glycerol supp (irritant action of glycerol stimulates)
4) Docusate sodium (stimulant and faecal softening action)
what are the important side effects associated with stimulant laxatives?
1) Abdominal pain or cramping common
2) With prolonged use, some stimulant laxatives cause melanosis coli (reversible pigmentation of the intestinal wall)
why are co-danthramer and co-danthrusate normally only prescribed for constipation in terminally ill patients?
potential carcinogenicity and evidence of genotoxicity.
1) Outline the MoA of faecal softeners
2) list 3 faecal softners
1) Act by decreasing surface tension and increasing penetration of intestinal fluid into the faecal mass.
2) Docusate sodium and glycerol suppositories, arachis oil (ground-nut oil, peanut oil)
who should stimulant laxatives not be prescribed to?
1) Avoid if intestinal obstruction is suspected as there is a risk that this could induce perforation
2) Rectal preparations are usually avoided if haemorrhoids or anal fissures are present.
How does the prescribing of stimulant laxatives differ in constipation and fecal impaction
1) For constipation, you should generally prescribe oral stimulant laxatives. Usually taken once or twice a day and the dose titrated to effect
2) Faecal impaction- rectal formulation should usually be prescribed once only or PRN with a max dose frequency of once in a 24-hour period.
when would Prucalopride be prescribed for constipation?
licensed for the treatment of chronic constipation in adults, when other laxatives have failed
what patient and carer advice should be provided to those prescribed ispaghula husk?
1) Always swallow with plenty of water and do not take immediately before bed. Full effect might take days to develop
2) dose should be taken with at least 150ml of water, preferably after meals, morning and evening
3) Potent allergens- may develop hypersensitivity reactions when handling
Methylcellulose is a bulk forming laxative which is indicated for constipation and diarrhoea. What advice should patients be provided regarding its use for these indications
1) Constipation: take with at least 300ml of liquid
2) Diarrhoea, ileostomy and colostomy control, avoid liquid intake for 30 minutes before and after dose
How long do the following take to work?
1) Docusate sodium (softning) - chronic constipation
2) Bisacodyl (stimulant)
3) senna (stimulant) (GSL 12 years+)
4) Sodium picosulfate (stimulant)
1) Docusate- Oral: 1-2 days | rectal :usually 20 minutes
2) Bisacodyl- Oral: 10-12 hours | rectal: 20-60 minutes
3) senna- Oral: 8-12 hours
4) Sodium picosulfate- Oral: 6-12 hours
