Constipation: Laxatives

Question 1

what is constipation?

Answer 1

Defaecation that is unsatisfactory because of:

1) Infrequent stools
3) Difficult stool passage
3) Seemingly incomplete defaecation

Question 2

who does constipation occur most commonly in? (3)

Answer 2

It can occur at any age and is commonly seen in:

1) Women
2) Elderly
3) Pregnancy

Question 3

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)

Answer 3

1) Anaemia
2) Abdominal pain
3) Weight loss
4) Blood in the stool

Question 4

Outline the diet and lifestyle advice given to those with constipation.

Answer 4

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

Question 5

Laxative abuse may lead to which electrolyte disturbance

Answer 5

Hypokalaemia

Question 6

List 4 classes of laxatives (4)

Answer 6

1) Bulk-forming laxatives
2) Stimulant laxatives
3) Faecal softeners
4) Osmotic laxatives

Question 7

What conditions are osmotic laxatives such as lactulose, macrogol and phosphate enemas indicated for? (3)

Answer 7

1) Constipation and faecal impaction.
2) Bowel preparation prior to surgery or endoscopy.
3) Hepatic encephalopathy (lactulose)

Question 8

Outline the MoA of osmotic laxatives

Answer 8

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.

Question 9

why is lactulose useful in the treatment of hepatic encephalopathy?

Answer 9

It produces an osmotic diarrhoea of low faecal pH, and discourages the proliferation of ammonia-producing organisms

Question 10

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?

Answer 10

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.

Question 11

which patient are osmotic laxatives contraindicated in?

Answer 11

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.

Question 12

What adverse drug interactions can occur with osmotic laxatives?

Answer 12

no significant adverse drug interactions but the effects of warfarin may be slightly increased

Question 13

state the dose of lactulose in an adult for the following:

1) Constipation
2) Hepatic encephalopathy

Answer 13

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.

Question 14

How long does it take for lactulose to work and who should it be used in caution with?

Answer 14

1) up to 48 hours to act

2) lactose intolerance, intestinal obstruction

Question 15

list 4 stimulant laxatives

Answer 15

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)

Question 16

what are the important side effects associated with stimulant laxatives?

Answer 16

1) Abdominal pain or cramping common

2) With prolonged use, some stimulant laxatives cause melanosis coli (reversible pigmentation of the intestinal wall)

Question 17

why are co-danthramer and co-danthrusate normally only prescribed for constipation in terminally ill patients?

Answer 17

potential carcinogenicity and evidence of genotoxicity.

Question 18

1) Outline the MoA of faecal softeners

2) list 3 faecal softners

Answer 18

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)

Question 19

who should stimulant laxatives not be prescribed to?

Answer 19

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.

Question 20

How does the prescribing of stimulant laxatives differ in constipation and fecal impaction

Answer 20

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.

Question 21

when would Prucalopride be prescribed for constipation?

Answer 21

licensed for the treatment of chronic constipation in adults, when other laxatives have failed

Question 22

what patient and carer advice should be provided to those prescribed ispaghula husk?

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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)

Answer 24

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