Constipation

Question 1

Bulk-forming Laxatives

Common indications

(Ispaghula husk, methylcellulose)

Answer 1

1. Constipation and faecal impaction- particularly in patients who cannot increase their dietary fibre intake
2. Mild Chronic diarrhoea- associated with diverticular disease or IBS

Question 2

Bulk-forming Laxatives

MOA

Answer 2

• Bulk-forming laxatives contain a hydrophilic substance, such as polysaccharide or cellulose, which is not absorbed or broken down by the gut.
• Like dietary fibre, this attracts water into the stool and increases its mass
• Adequate fluid intake is therefore important to the action of bulk-forming laxatives
• Increased stool bulk stimulates peristalsis and helps releive constipation
• It can also help in chronic diarrhoea or when stoma output needs managing

Question 3

Bulk-forming Laxatives

Important adverse effects

Answer 3

• These drugs are generally well tolerated, with mild abdominal distension and flatulence being the most common side effect.
• Rarely, they can cause GI obstruction and faecal impaction

Question 4

Bulk-forming Laxatives

Warnings

Answer 4

• They should not be used in patients with subacute or established intestinal obstruction or faecal impaction
• And in general should not be used in patients with ileus

Question 5

Bulk-forming Laxatives

Administration

Answer 5

• Bulk-forming laxatives may be provided in the form of granules or powder to be dissolved in water or tablets
• Importantly, they should be taken with plenty of water (300mL)

Question 6

Bulk-forming Laxatives

Communication and monitoring

Answer 6

• Explain that you are offering a laxative that works as a fibre supplement
• This will hopefully make there stools easier to pass
• Outline the common side effects
• Tell them the dose can be adjusted according to there symptoms
• Take at mealtimes
  
  • When treating inpatients, a stool chart is useful to monitor efficacy of treatment

Question 7

Osmotic Laxatives (lactulose, macrogol, phosphate enema)

Common indications

Answer 7

• Constipation and faecal impaction
• Bowel preparation prior to surgery or endoscopy
• Hepatic encephalopathy

Question 8

Osmotic Laxatives (lactulose, macrogol, phosphate enema)

MOA

Answer 8

• These medicines are based on osmotically active substances (sugars or alcoho.ls) that are not absorbed or digested, therefore remain in the gut lumen.
• They hold water in the stool, maintaining its volume and stimulating peristalsis.
• Lactulose, in particular also reduces ammonia absorption (Hepatic encephalopathy)
• It does this by increasing gut transit rate and acidifying the stool, which inhibits the proliferations of ammonia-producing bacteria, hence is helpful in people in liver failure

Question 9

Osmotic Laxatives (lactulose, macrogol, phosphate enema)

Important adverse effects

Answer 9

• Flatulence, abdominal cramps and nausea are common
• Diarrhoea
• Local irritation
• Electrolyte disturbances

Question 10

Osmotic Laxatives (lactulose, macrogol, phosphate enema)

Warnings

Answer 10

• Lactulose is contra-indicated in Intestinal obstruction as there is a risk of proliferation
• Phosphate enemas can cause significant fluid shift so should be used with caution in those patients with HF, ascites and when electrolyte disturbances are present

Question 11

Osmotic Laxatives (lactulose, macrogol, phosphate enema)

Important interactions

Answer 11

• There are no significant interactions
• However the effects of warfarin may be slightly increased

Question 12

Osmotic Laxatives (lactulose, macrogol, phosphate enema)

Communication

Answer 12

• Explain that you are offering treatment with a laxative that will hopefully make their stool softer and easier to pass
• To work, it requires them to drink plenty of water. They should aim for 6-8 glasses a day
• Mention ab cramps and flatulence can occur but should get better over time

Question 13

Stimulant laxatives (bisacodyl, senna, glycerol, docusate)

Common indications

Answer 13

1. Constipation
2. Faecal impation- only in suppository form

Question 14

Stimulant laxatives (bisacodyl, senna, glycerol, docusate)

MOA

Answer 14

• Stimulant laxatives increase water and electrolyte secretion from the colon mucosa, thereby increasing volume of colonic content and stimulating peristalsis
• They also have a direct pro-peristalsis action with the mechanisms varying between formulations
• Senna gets metabolised by bacteria with the metabolite have a direct action of the enteric nervous system
• Docusate has both stimulant and faecal softening actions

Question 15

Stimulant laxatives (bisacodyl, senna, glycerol, docusate)

Adverse effects

Answer 15

• Ab pain/cramps
• Prolonged use can cause melanosis coli (reversible pigmentation of intestinal wall)
• Prolonged use can also cause lazy bowel

Question 16

Stimulant laxatives (bisacodyl, senna, glycerol, docusate)

Warnings

Answer 16

• These are contraindicated in patients with intestinal obstruction due to the risk of perforation
• Rectal preparations should be avoided if haemorrhoids or anal fissures are present

Question 17

Methylnaltrexone

Indications

Answer 17

• Opioid induced constipation in patients with chronic pain- 12mg OD PRN
• Adjunct to other laxatives in opioid-induced constipation in palliative care- NB for this indication it is based on weight

Question 18

Methylnaltrexone

MOA

Answer 18

• Methylnaltrexone is a peripherally acting opioid receptor antagonist
• Therefore blocks the GI (constipating) effects of opioids without altering their central analegesic effects

Question 19

Methylnaltrexone

Adverse effects

Answer 19

• Opioid withdrawal like-symptoms
• N&V- GI disturbances
• Orthostatic hypotension is a symptom of overdose

Question 20

Methylnaltrexone

warnings

Answer 20

• Contraindicated: Acute GI surgery, GI obstruction
• Cautioned: Faecal impaction, diverticular disease, colostomy