Constipation

Question 1

What are some stimulant laxatives?

What is their onset?

What is their place in therapy?

Answer 1

• Senna
• Bisacodyl

6hr - 12 hrs (oral)
15 min - 60 min (suppository)
5 min - 15 min (enema)

Commonly used in combination with a softener. Avoid use in patients with bowel obstruction with colic, as stimulants increase peristalsis and may worsen colic or cause perforation.

Question 2

What are some softening laxatives?

What is their onset?

What is their place in therapy?

Answer 2

• Docusate

1 to 3 days

These have limited use if used alone, a stimulant is usually needed in combination.

Question 4

What are some osmotic agents?

What is their onset?

What is their place in therapy?

Answer 4

• Macrogrols or polyethylene glycol (molaxole)
• Variable depending on severity 2 to 4 days
• Lactulose
• 1 to 2 days

Can be used in addition if a stimulant with softener is ineffective, or can be used alone if a stimulant is contra-indicated or not tolerated. Macrogols are preferable to lactulose in palliative care. Lactulose is associated with abdominal cramps, bloating and nausea.

Question 6

What is constipation?

Answer 6

Constipation is generally described as infrequent defecation (usually <3 times/week), often with straining and passage of hard, uncomfortable stools

Question 7

What is a combination stimulant and softener?

What is their onset?

What is their place in therapy?

Answer 7

Docusate and senna

• 6 to 12 hours

Avoid use in patients with bowel obstruction with colic, as stimulants increase peristalsis and may worsen colic or cause perforation.

Question 8

Stool softener (docusate)

What is the mode of action?

What is the indication?

Answer 8

• Softens stool, acts by lowering the surface tension of the stool, allowing water and salts into the hardened stool. May also increase intestinal fluid secretion
• Constipation (includes combination with senna) Prevent straining following rectal surgery
• They have little value as single agents in chronic constipation or constipation from opioid use

Question 9

Stimulant Laxative (Bisacodyl, Senna)

What is the mode of action?

What is the indication?

Contraindication?

Answer 9

a stimulant laxative, acts directly on intestinal mucosa to stimulate peristalsis and induce fluid secretion into colon contents, which enhances movement of bowel motions through the colon.

Constipation

Intestinal obstruction, partial or complete

Question 10

Osmotic Laxative (macrogols or Polyethylene glycol PEGs)

What is the mode of action?

What is the indication?

Answer 10

Macrogol is an osmotically acting laxative; that is, an inert substance that passes through the gut without being absorbed into the body. It relieves constipation because it causes water to be retained in the bowel instead of being absorbed into the body.

constipation and faecal impaction

Question 11

What are some dietary and lifestyle advice?

Answer 11

Increasing the fibre content of the diet will increase the frequency of bowel motions in constipated patients. A high fibre diet consists of 18-30 g fibre per day from fruit, vegetables, wholemeal bread, cereals and grain foods. Oat bran or unprocessed bran can be taken with food or fruit juice. Benefit may be apparent in three to five days but the diet should be tried for at least a month.

Maintaining fluid intake should help prevent constipation. Two litres of water daily is recommended for people on a high fibre diet. Avoid a high fibre diet if adequate fluid intake is not possible.

Regular exercise encourages peristalsis in the colon and should be part of a management plan for constipation

A high fibre diet is generally less effective if constipation is secondary to slow transit (reduced gut motility). Constipation secondary to opioid analgesic use usually requires more aggressive management than just fibre supplementation.

Question 12

Constipation ‘Red Flags’ which may indicate the need for further investigation

Answer 12

• Blood in the stools
• New onset or worsening constipation in people aged over 50
• Concurrent weight loss, nausea, vomiting, anorexia or fever
• Severe abdominal pain
• Co-existing or alternating diarrhoea
• Persistent symptoms
• Tenesmus
• Failure of laxative treatment and lifestyle modifications

Question 13

Osmotic Laxative (Lactulose)

What is the mode of action?

Answer 13

Lactulose is metabolized in the colon by colonic bacteria to monosaccharides and then to volatile fatty acids, hydrogen, and methane. Lactulose reduces intestinal ammonia production and absorption in 3 ways. Finally, lactulose also causes a reduction in intestinal production of ammonia

Attract large amounts of water into the bowel, making the stool soft, loose and easier to pass

Question 14

What are some bulking agents?

What is their onset?

What is their place in therapy?

Answer 14

Psyllium (Konsyl D, Mucilax, metamucil)

2 to 3 days

Question 15

Choosing a laxative

Constipation caused by opioid analgesic?

Answer 15

Constipation caused by an opioid analgesic will usually require a laxative which includes a stimulant such as senna. A bulk former used in this situation could lead to impaction and a stool softener or osmotic preparation would not solve the underlying problem of reduced gut motility.

Question 16

Choosing a laxative

Intestinal obstruction

Answer 16

Generally, all oral laxative preparations should be avoided in people with intestinal obstruction but there is evidence of safe and effective use of macrogols in malignant obstruction

Question 17

Choosing a laxative

Fecal softeners

Answer 17

These agents lower surface tension and allow water to penetrate hard dry faeces.

Softeners are often combined with a stimulant where they are especially useful for opioid induced constipation. Enemas are also available to give a more rapid action.

Docusate is a faecal softener with some stimulant activity. Oral docusate should be avoided in people with intestinal obstruction.

Question 18

Choosing a laxative

Osmotic Laxative

Answer 18

These work in the lumen of the colon to draw water in to the gut by osmosis. Osmotic laxatives need to be taken in combination with a good fluid intake.

Lactulose, an osmotic laxative, is fermented by gut bacteria to produce short chain fatty acids with resultant beneficial effects on gut motility and flora. It is a synthetic combination of galactose and fructose which is not absorbed in the gastrointestinal tract and can be taken by people with diabetes (avoid in those with galactosaemia). It needs to be taken regularly and takes at least two or three days to work so will not give immediate relief. Abdominal discomfort and flatulence are common side effects and some people find it unpalatable.

Macrogols (e.g. Movicol) are relatively new products and appear to be at least as effective as lactulose and may cause less flatulence. However, there is no evidence that they are more effective or superior to more established, less expensive agents. Macrogols should be avoided in people with severe inflammatory conditions of the gut (e.g. Crohn’s disease, ulcerative colitis, toxic megacolon).

Question 19

Choosing a laxative

Stimulant Laxative

Answer 19

These increase intestinal motility by direct stimulation of colonic nerves to increase the movement of faeces. They are often suitable for short term use to restore normal bowel function and are usually taken at night to produce an effect the next morning.

Bisacodyl stimulates small as well as large bowel motility. Bisacodyl suppositories can be used for rapid evacuation.

Senna is available in combination with faecal softeners and is especially useful in longer term management of opioid induced constipation. The use of danthron containing preparations is restricted to terminal care due to concerns about its potential for carcinogenicity.

Abdominal cramps are common with stimulants and they should be avoided if there is a possibility of intestinal obstruction. Prolonged use of stimulant laxatives can lead to diarrhoea and associated fluid and electrolyte imbalance (e.g. hypokalemia) particularly if fluid intake is inadequate.

Question 20

Choosing a laxative

Rectal preparations (suppositories and enemas)

Answer 20

These are used if oral preparations are ineffective or if impaction is low down the intestinal tract. Avoid rectal preparations if haemorrhoids or anal fissures are present.

The choice of product is governed by the site of the impaction and stool type.2

Phosphate enemas (e.g. Fleet) are suitable for hard impacted stools
Bisacodyl suppositories can be used for soft stools in the lower rectum
Glycerol suppositories are often effective for both soft and hard stools in the lower rectum
Docusate enemas (e.g. Coloxyl) can be used for clearing both hard and soft stools occurring higher in the rectum

Question 21

What are some causes of constipation?

Answer 21

• poor diet (low fibre and low fluid intake)
• Immobility
• stress
• supressing the urge to defecate
• drugs (The main mechanism is slowing of gut motility due to anticholinergic or antispasmodic effects)