Laxatives and the Management of Constipation

Constipation may be defined as the uncomfortable, infrequent passage of hard faeces.¹ The condition is believed to affect 25% of the general population² and is most common in young women,³ the elderly and terminally ill patients.⁴ Most cases of constipation can be managed in the community with reassurance, lifestyle changes and laxative therapy.³

Consideration should be given to conditions which predispose to constipation such as such as poor fluid and dietary fibre intake, immobility, drugs, functional or obstructive bowel disorders, neurological diseases, metabolic conditions and depression. A full history and examination including digital rectal examination may reveal underlying conditions.⁴ Colorectal cancer must be considered in older people with altered bowel habit and cases referred to secondary care for urgent colonoscopy where appropriate.⁵ However most patients can be managed in primary care using simple measures.³

Lifestyle changes⁴

Advice should be given regarding basic lifestyle alterations. Patients should be encouraged to,

• Adopt a high-fibre diet
• Increase water intake to 2 litres per day
• Exercise more frequently

Lifestyle interventions should be continued for a month before reassessment, as their full effects are often delayed.

Behavioural therapy²

Behavioural therapy and habit training are effective therapies for patients with slow gut transit, impaired rectal emptying, pelvic floor abnormalities, rectoceles and mild neurological disease, in whom traditional treatments have failed. Therapy involves sphincter function biofeedback exercises, psychological support and assistance to discontinue laxatives. These new treatments have shown promising long-term outcomes and are gaining popularity.

All medications, including over the counter preparations should be reviewed. If possible, any causative drugs should be stopped or dosages reduced.⁴

Laxatives

Laxatives are recommended when:⁶

• Dietary measures fail
• While dietary measures take effect
• For drug-induced constipation
• Where prolonged straining at stool may be dangerous e.g. angina or haemorrhoids
• Before surgery and radiological procedures
• To assist expulsion of parasites after anthelmintic treatment

There is little evidence on which to base recommendations for laxative selection. It is reasonable to base individual choices on the severity of symptoms, stool consistency, patient preference and cost. The lowest effective dose should be prescribed and reduced once symptoms improve. Oral preparations should be used whenever possible but short courses of rectal laxatives may be appropriate if oral treatments have failed or rapid relief of rectal loading is required. Rectal laxatives should be avoided if haemorrhoids or anal fissures are present.⁴ Manual evacuation may be necessary if all pharmacological interventions fail.¹
Laxatives can be divided into 4 main groups. An understanding of the basic mechanisms of action assists in the selection of appropriate drugs.¹

Bulk-forming laxatives

Bulk-forming laxatives retain water within stools and increase faecal mass, thus stimulating peristalsis, e.g. ispaghula, methylcellulose. An adequate water intake is necessary to avoid worsening constipation and intestinal obstruction.⁶ Full effects may take several days so they are inappropriate for acute relief of constipation.⁴
Bulk-forming laxatives are useful in the management of patients with small, hard stools and those with stomas, haemorrhoids, anal fissures, diverticular disease, irritable bowel syndrome and as an adjunctive treatment of ulcerative colitis.⁶ Patients may complain of flatulence, bloating and abdominal distension but side-effects usually settle with continued use.⁴

Stimulant laxatives

These drugs induce intestinal peristalsis by direct stimulation of the myenteric plexus e.g. bisacodyl®, docusate sodium, senna, danthron®.¹ Stimulant laxatives are popular because of their rapid effect but will often cause abdominal cramps. Rectal preparations of stimulant laxatives are useful for prompt evacuation of impacted stools. Bisacodyl® suppositories are used to evacuate soft stools from the lower rectum. Glycerol suppositories will eliminate soft or hard stools from the lower rectum and docusate sodium enemas will clear faeces from the upper rectum.⁴ Stimulant laxatives must be avoided in bowel obstruction as they may lead to perforation. Long-term use of high-doses can cause diarrhoea with significant fluid and electrolyte imbalances, however prolonged therapy is sometimes necessary.⁶ All preparations containing danthron such as co-danthramer and co-danthrusate should be restricted to terminally ill patients due to concerns regarding genotoxicity.⁴

Faecal softeners

Faecal softeners act by decreasing the surface tension of stools and facilitating infiltration of intestinal fluid e.g. arachis oil, docusate sodium (which has stool-softening properties in addition to its stimulant effects).⁴ These drugs are useful for oral administration in the management of haemorrhoids and anal fissures as they will soften and lubricate faecal material.⁶
Arachis oil enemas are also useful in the management of patients with hard, impacted stools. Liquid paraffin is not recommended as it can cause anal seepage and irritation, lipoid pneumonia and malabsorption of fat-soluble vitamins.⁴

Osmotic laxatives

Osmotic laxatives act by increasing the amount of water in the large bowel e.g. lactulose, polyethylene glycols, rectal phosphates.
Variable time is needed to achieve their full effects. An adequate fluid intake is necessary to prevent dehydration and some preparations such as polyethylene glycols are administered with fluid to avoid this problem. Phosphate enemas are useful for clearance of hard, impacted stools and for bowel evacuation before surgery and radiological or endoscopic investigations. Osmotic laxatives must not be used in bowel obstruction and polyethylene glycol should be avoided in patients with severe inflammatory conditions of the gastrointestinal tract such as Crohn's disease or ulcerative colitis.⁴

Future drug therapy

Recent work has focused on the development of specific 5HT₄ receptor agonists. In contrast to conventional laxatives, which act through luminal mechanisms these prokinetic agents are absorbed in the small intestine and systemically stimulate intestinal peristalsis. Tegaserod is already licensed in the United States² and a similar drug prucalopride is currently undergoing clinical trials.⁷

The outcome of colectomy for intractable constipation is unpredictable and is now only rarely performed. Patients with severe idiopathic constipation may benefit from chronic percutaneous sacral nerve stimulation, which is used to modify bowel neuromuscular control. It is hoped that new interventional and pharmacological techniques will further reduce the need for bowel resections.

Children

Constipation is common in children accounting for 25% of the paediatric gastroenterologists work load.⁸ Constipation in children may be due to physical disorders, diet, medicines, or stress. However, there are some important diagnoses that need to be excluded. The following table lists a few of these conditions:

Infrequent defaecation increases the likelihood of pain on passage of hard stools, anal fissures, anal spasm and ultimately a learned response to withhold defaecation. Mild constipation may be relieved by increased fluid and dietary fibre intake. If necessary an osmotic or bulk-forming laxative may be prescribed. Stimulant laxatives can also be used but may precipitate colic, diarrhoea and overflow incontinence.^4,8

Chronic obstruction may cause the rectum to enlarge to form a megarectum, which has impaired sensation and decreased contractility, resulting in soiling. If the bowel is impacted and cannot be cleared using oral laxatives, specialist referral for bowel cleansing solutions, suppositories, enemas or manual evacuation is recommended.⁹

Regular bowel actions must then be established using dietary advice (fibre and fluid intake), regular laxatives (e.g. lactulose) and encouragement of a toileting pattern. Laxatives must be continued for many months and then gradually withdrawn. Relapses are common and should be treated early with increased doses of laxatives.⁴ Children and parents should be offered psychological counselling and support through the treatment process. Older children may also benefit from biofeedback training.⁹
Very rarely children may requires enemas under sedation and even surgery to modify the anal sphincter.⁸

There have been several attempts at the production of guidelines although no consensus as yet. There is a good algorithm from Guy's and St Thomas' hospital.⁸

Pregnancy and Breast-feeding

• Constipation is common during late pregnancy. A higher dietary fibre and fluid intake increases the frequency of defaecation and produces softer stools but drug treatment is sometimes required.¹⁰ Little trial data is available regarding the safety of laxatives during pregnancy and breast-feeding but most are considered safe for short-term use.⁴
• Bulk-forming laxatives are recommended as first line therapy during pregnancy, as they are generally well tolerated. If these are ineffective, stimulant or osmotic laxatives may be considered. Stimulant laxatives are effective but may cause abdominal pain and diarrhoea. Senna may be used for short periods but should be prescribed with caution in the third trimester as it may stimulate uterine contractions. Few studies have evaluated the efficacy of osmotic laxatives.⁴
  Bulk-forming laxatives and lactulose are considered safe during breast-feeding, as they are not systemically absorbed. Senna enters breast-milk and high-doses may cause colic and diarrhoea in infants. Sodium and phosphate enemas are best avoided during both pregnancy and breast-feeding as they can cause fluid and electrolyte imbalances.⁴

Terminally ill patients

• Constipation is common in patients who are terminally ill, particularly those with advanced cancer. It is often caused by immobility, drugs and reduced fluid and dietary intake but may also be due to conditions such as hypercalcaemia, intra-abdominal disease or spinal cord compression.¹
  
  
• The management of constipation involves advice on diet, fluid intake, mobility and pain control combined with the use of laxatives.¹ High-fibre diets and bulk-forming laxatives are not recommended for patients taking opiates or with a poor fluid intake due to the risk of intestinal obstruction.⁴ Efforts should be made to prevent constipation in patients on opiate treatment, by regular administration of laxatives.⁶
• Stimulant laxatives such as senna or docusate sodium may be used when the colon is loaded or the rectum contains soft faeces. A laxative with faecal softening actions such as docusate sodium or co-danthramer is more appropriate when hard faeces are impacted in the rectum.⁴