Causes of constipation
- dietary insufficiency → lack of fibre, dehydration
- reduced mobility
- malignant disease
- weakness/fatigue
- bowel obstruction
- clinical depression
- endocrine/metabolic disorders → diabetes, hypercalcaemia, hypothyroidism
- neurological disorders → MND, Parkinson’s
- Drug - induced → opioids, chemotherapy, antacids, anticholinergics, antidepressants, antihistamines, diuretics, iron supplements, NSAIDs
- environmental → lack of privacy/toilet availability
- pain on defecation
Symptoms of constipation
- abdominal pain
- anorexia
- early satiety
- nausea/vomiting
- abdominal distention
- diarrhoea (overflow)
- flatulence
- halitosis
- headache
- intestinal obstruction/impaction
- intestinal perforation
- haemorrhoids
- urinary retention
Bristol stool chart
Hx and examination/Ix in a patient with constipation
- Previous/usual bowel habit
- change in bowel habit → frequency, consistency, medication, difficulty, pain
- full medical Hx
- surgical Hx
- Drug Hx
- abdominal exam - presence of faecal mass
- bowel auscultation
- PR → to identify haemorrhoids, rectal prolapse, anal tone, faecal impaction
- Bloods: anaemia, TFTs, hypercalcaemia, glucose and electrolytes
How to address reversible causes of constipation?
- stop or reduce constipating drugs (if possible)
- encourage mobility
- encourage diet and fluids
- ensure privacy
- the correct position for opening bowels (where possible)
Stimulant laxatives
- MoA
- examples
MoA: stimulates colonic nerves → more peristalsis → foecal mass can move
Examples:
- Senna (tablets/liquid)
- Glycerol suppositories (also soften)
- Sodium Pico Sulphate
- Dantron*
Dantron is used only in palliative patients (but not in faecal incontinence as it can burn)
Side effects of stimulant laxatives
- abdominal cramps
- not to be used in bowel obstruction (!)
- Dantron (only used in palliative patients) → burns and changes urine colour
Osmotic laxatives
- MoA
- Examples
MoA: draw and retain water in large bowel through osmosis
Examples:
- Macrogol
- Lactulose
- Phosphates
Cautions and SEs of osmotic laxatives
- patient needs to be able to drink enough fluids
- Lactulose → causes flatulence and cramps
- Contraindications: ileus, bowel obstruction (or at risk of), severe inflammatory conditions (e.g. Crohn’s, UC)
Usual medication regime for a constipated patient
stimulant + softener
MoA and example of stool softener
MoA: reduce surface tension of a stool as it allows water to penetrate it
Example: Docusate sodium
*can be used in bowel obstruction
The only type of anti-constipation drug that can be used in bowel obstruction
Stool softener e.g. Docusate sodium
MoA and examples of bulk laxatives
MoA: absorb water and expand in the bowel → stool mass increases → bowel stretched and stimulated
- water retained to soften hard stools
- bulk to make liquid stool more solid
Example: Ispaghula husk (Fybogel)
Contraindications and caution for bulk laxatives use
Contraindications:
- bowel obstruction
- faecal impaction
- undiagnosed rectal bleeding
- sudden change in bowel habits >2 weeks
Caution: with opioid use
Class of movicol
Osmotic laxative
Management of:
impacted hard faeces in the rectum
- 1st line: Bisacodyl suppository (stimulant laxative) + glycerol suppository + oral laxative
- 2nd line: enema
Management of:
Impacted soft faeces in the rectum
- 1st line: Bisacodyl suppository + oral stimulant laxative
- 2nd line: enema
Management of:
Empty rectum plus colon loaded with faeces
Phosphate enema + combination oral laxatives
What should be all patients on opioids prescribed?
stimulant laxative
What drug to consider in Mx of constipation if oral laxatives and rectal interventions fail?
Methylnaltrexone
- It is peripherally acting opioid receptor antagonist
- It decreases the constipating effects of opioids
*can be given S/C or PO
Contraindicated in: acute surgical conditions and intestinal obstruction
