Constipation and laxative prescribing

• 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.
• Constipation is more common in the elderly population and in women
• Chronic constipation complications:

  • Faecal loading/impaction
  • Faecal incontinence
  • Haemorrhoids
  • Anal fissures
  • Rectal bleeding
• Emergencies from constipation include bowel obstruction and bowel perforation
• Examination:

  • Abdominal exam - assessing for masses, tenderness and signs of peritonitis
  • Rectal exam - haemorrhoids, fissures or hard stool
  • Basic observations
  • Assessing hydration status
• Underlying medical conditions:

  • Endocrine disorders e.g. hypothyroidism (slowed metabolism and reduced peristalsis)
  • Neurological disorders - MS (reduced/absent autonomic sensory and motor responses)
  • Myopathic diseases
  • Structural abnormalities e.g. haemorrhoids, anal fissures (causing pain and stool holding)
• Iatrogenic causes:

  • Opioids
  • Iron supplements
  • Tricyclic antidepressants
  • Antipsychotics
• Constipation in pregnancy is common and occurs due to the increase in progesterone, which relaxes intestinal smooth muscle.
• Psychological causes:

  • Anxiety and depression (causing altered/reduced intake, reduced movement)
  • Eating disorders (poor oral intake and/or laxative abuse creating dependence)
• IBS can cause constipation and recurrent abdominal pain. The Rome IV criteria is used to diagnose IBS.
• Bulk forming laxatives:

  • E.g. ispaghula husk (Fybogel) and methylcellulose (Celevac)
  • Bulk out the stool with soluble fibre
  • Increased faecal mass and stimulates peristalsis
  • Onset of action up to 72 hours
  • Common side effects: flatulence, bloating and cramping
  • Patients need to increase fluid intake while taking
• Osmotic laxatives:

  • Lactulose (Movicol) and macrogols (Laxido)
  • Draw water via osmosis into the stool
  • Side effects: cramps, diarrhoea, nausea and vomiting
  • Lactulose is used to treat hepatic encephalopathy as it reduces the intestinal production and absorption of ammonia
• Stimulant laxatives:

  • Senna (Senokot), Bisacodyl (Dulcolax) and sodium picosulfate
  • Stimulate the nerves of the digestive tract to cause peristalsis
• Stool softening laxatives:

  • E.g. docusate
  • Stool softening laxatives decrease the surface tension of faecal mass and increase intestinal fluid in the stool
• 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. 
• 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
• 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
• 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)
• 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

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