Prescribing Laxatives

Introduction

Laxatives are used to treat constipation in patients. Prescribing laxatives is a common task for all clinicians and frequently appears in medical school exams and the Prescribing Safety Assessment (PSA).

This article will cover the different types of laxatives and how to approach prescribing laxatives. Always check and follow local guidelines and refer to the BNF before prescribing. 

Constipation

Constipation is a symptom-based disorder where patients describe problematic defecation because of infrequent stools, hard stools, difficulty passing stools or sensation of incomplete emptying of stool.

In practice, it is often defined as when a patient passes stools less frequently than their normal pattern.¹ It is worth noting that many patients define constipation as ‘hard stool’, with no reference to frequency.

Constipation is more common in the elderly population, and the incidence of constipation is 2-3 times higher in women than in men. The UK primary care cohort study found the prevalence of GP-diagnosed constipation was 12.8/1000 people. However, prevalence is thought to be much higher because people appropriately self-treat using over-the-counter remedies and medications rather than consulting healthcare professionals.¹

Constipation rarely causes complications or long-term health problems, and treatment is usually effective, especially when given promptly.² Chronic constipation is more likely to cause complications and medical emergencies. Complications include faecal loading/impaction, faecal incontinence, haemorrhoids, anal fissures, and rectal bleeding. Emergencies include bowel obstruction and bowel perforation.

Causes of constipation

If a patient presents with constipation, consider the causes of the constipation.

Identifying any associated symptoms (e.g., abdominal pain, weight loss, fatigue) that may indicate a sinister underlying condition such as gastrointestinal malignancy is important. These red-flag symptoms require further investigation, including blood tests and qFIT testing.

The examination of a constipated patient will depend on the clinical context but may include:

• Abdominal examination: this may assist in identifying the cause of constipation (e.g. deeper abdominal masses); it will also assess for abdominal tenderness and signs of peritonitis
• Rectal examination: this may identify the causes of constipation (e.g. if there are any fissures or haemorrhoids); it will also assess for hard stool in the rectum
• Basic observations (vital signs): may be useful if assessing an acutely unwell patient with constipation to check for haemodynamic stability or if there are any associated fevers
• Assessing hydration status: assessing hydration could be helpful when considering if dehydration may be the cause/contribution of constipation

Underlying medical condition

Constipation can be caused by an underlying medical condition (i.e., secondary constipation). Examples include:

• Endocrine disorders: hypothyroidism (causing slowed metabolism and reduced peristalsis)
• Neurological disorders: multiple sclerosis (causing reduced/absent autonomic, sensory and motor responses)
• Myopathic diseases: myotonic dystrophy (causing muscle weakness/spasm)
• Structural abnormalities: haemorrhoids, anal fissures (causing pain and stool holding)

Iatrogenic causes

Constipation can be caused by a variety of medications (iatrogenic constipation). Examples include:

• Opioids
• Iron supplements
• Tricyclic antidepressants
• Antipsychotics

Pregnancy

Constipation in pregnancy is common and occurs due to the increase in progesterone, which relaxes intestinal smooth muscle.

Psychological causes

Psychological causes of constipation include:

• Anxiety and depression (causing altered/reduced intake, reduced movement, altered muscle reflexes/sensitivity)
• Somatisation disorders (causing altered neuromuscular response in the bowel)
• Eating disorders (from poor intake and/or laxative abuse creating dependence)

Types of laxative

Laxatives have different modes of action and are not necessarily interchangeable. When prescribing laxatives, it is essential to consider the reason for constipation and choose the appropriate laxative. 

In the community, some laxatives can be bought over the counter from pharmacies, and others require a medical prescription.

Bulk-forming laxatives

Examples: ispaghula husk (Fybogel), methylcellulose (Celevac)

Bulk-forming laxatives ‘bulk out’ the stool with soluble fibre. This increases faecal mass and stimulates peristalsis. Their onset of action is up to 72 hours, and common adverse effects include flatulence, bloating and cramping.

Patients should be advised to increase fluid intake when taking bulk-forming laxatives. 

Osmotic laxatives

Examples: lactulose, macrogols (Movicol, Laxido)

Osmotic laxatives draw water via osmosis into the stool, making it softer and easier to pass. Adverse effects include abdominal cramps, diarrhoea, nausea and vomiting.

Stimulant laxatives

Examples: senna (Senokot), bisacodyl (Dulcolax), sodium picosulfate

Stimulant laxatives stimulate the nerves of the digestive tract to cause peristalsis.

Stool softening laxatives

Examples: docusate

Stool softening laxatives decrease the surface tension of faecal mass and increase intestinal fluid in the stool.

Other

Glycerol suppositories are both a lubricant and a rectal stimulant. 

Prokinetic laxatives are selective serotonin receptor agonists which stimulate intestinal motility. These should only be used under specialist advice. 

Prescribing laxatives

Do not prescribe laxatives for patients with suspected bowel obstruction or perforation.

Before advising or prescribing the medical treatment of laxatives, consider lifestyle advice:

• Increasing calorie intake
• Body position when passing stool
• Increased dietary fibre (vegetables, fruit, bran etc)
• Increased movement and exercise
• Ensure adequate hydration

Short term constipation

For patients with short-term onset constipation:

Step 1: Start bulk-forming laxative

Step 2: Add or switch to an osmotic laxative

Step 3: Add stimulant laxative

Opioid-induced constipation

For patients with opioid-induced constipation:

Step 1: Start osmotic laxative and stimulant laxative

Step 2: Add softener laxative

Step 3: Naloxegol (mechanism: opioid receptor antagonist)

Faecal impaction⁴

For patients with faecal impaction (i.e. retention of faeces to the extent that spontaneous evacuation is unlikely), consider oral macrogol/oral stimulant laxative depending on stool consistency.⁴

If there is an inadequate response to oral laxatives, consider rectal administration of bisacodyl/glycerol.

Chronic constipation

For patients with chronic constipation (constipation symptoms for at least three months):⁵

Step 1: Start bulk-forming laxative

Step 2: Add or change to osmotic laxative

Step 3: Add stimulant laxative

If at least two laxatives from different classes have been tried, prucalopride can be trialled in women only.

In chronic constipation, always gradually withdraw treatment. In addition, electrolytes should be monitored as there is an increased risk of derangement (e.g. hypokalemia).

Pregnant/breastfeeding women

In pregnant/breastfeeding women– dietary and lifestyle are important to try first, including considering fibre supplements. Bulk-forming laxatives are considered the first line. Always consult the BNF for details if bulk-forming laxatives are not effective.

Reviewer

Dr Seb Pillon

GP and Primary Care Medical Educator

Editor

Dr Chris Jefferies

References

1. NICE CKS. Constipation – background information. Published in 2023. Available from: [LINK]
2. NHS Inform. Constipation. Published in 2023. Available from: [LINK]
3. MDCalc. Rome IV Diagnostic Criteria for Irritable Bowel Syndrome (IBS). Available from: [LINK]
4. BNF. Constipation | Treatment summaries. Available from: [LINK]
5. NICE CKS. Constipation – definition. Published in 2023. Available from: [LINK]