Disease - Laxatives

From CambridgeNotes

Constipation, defined as the infrequent, difficult passage of small hard faeces, is a common problem in terminal disease. It is associated with bloating, abdominal pain, flatulence and the complications of anorexia, overflow diarrhoea, nausea and vomiting and urinary dysfunction.

Causes of constipation:

  • Drugs: opioids, anti-emetics cyclizine and ondansetron, anti-cholinergics, NSAIDs
  • Debility: weakness, immobility, poor nutrition/fluid intake, confusion
  • Cancer: hypercalcaemia, spinal cord compression, cauda equina syndrome, depression, intra-abdominal or pelvic disease e.g. tumour causing intestinal obstruction.
  • Co-morbidities: haemorrhoids, anal fissure, endocrine dysfunction

Management of constipation: Aim is to achieve comfortable defecation.

1) Non-medical: high fibre diet, increased fluid intake, increased mobility and toileting.

2) Medical: Laxatives. The following groups of laxatives are available:

  • Predominantly softening laxatives
    • Surfactants: docusate, poloxamer
      • Action: increases water penetration by acting as a detergent
      • Indications: opioid induced constipation, intermittent bowel obstruction
      • Preparations:
        • co-danthrusate: softener (docusate) + stimulant (dantron)
        • co-danthramer: softener (poloxamer) + stimulant (dantron)
    • Osmotic laxatives: lactulose
      • Action: draws water into the bowel, latency of action is up to 3 days
      • Side effects: bloating, abdominal pains/colic, flatulence
      • Preparations: liquid, very sweet to taste, needs increased fluid intake
    • Bulk-forming agents: ispaghula (if dietary fibre cannot be increased)
      • need large volumes of water to work and risk of worsening an incipient obstruction, so are less helpful
    • Saline laxatives: magnesium sulphate, milpar (magnesium hydroxide + liquid paraffin)
      • strong purgative action
  • Predominantly stimulating laxatives
    • senna, dantron
    • Action: stimulate the myenteric plexus directly to promote peristalsis and reduce net absorption of water and electrolytes in the colon.
    • Indications: opioid induced constipation, use with stool softeners e.g. senna + lactulose combination
    • Latency of action is 6-12 hours
    • Side effects
      • Senna: GI cramps, hypokalaemia
      • Dantron: GI cramps, peri-anal rash, pink/red discolouration of urine
    • Contra-indicated if GI obstruction
  • Rectal laxatives
    • Sometimes necessary alongside an oral laxative, but should not be part of regular treatment as they are inconvenient and may reduce quality of life
    • Bisacodyl suppository: rapidly stimulates evacuation of soft stool from a lax rectum
    • Glycerine suppository: softens hard stool
    • Phosphate enema: evacuates stool from lower bowel
    • Lubricant arachis oil enema: softens hard, impacted stools (overnight)
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