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Laxatives

Constipation vs impaction — laxative ladder & disimpaction

Always rule out bowel obstruction before prescribing laxatives. Determine if there is faecal impaction (PR exam). Opioid-induced constipation requires a stimulant laxative (senna) from day one — not osmotic alone.

What to do

1 · Rule out obstruction

Ask: vomiting? abdominal distension? no flatus? colicky pain? If yes to any: examine, AXR, and do NOT prescribe laxatives without senior review.

2 · Identify cause

Opioids, dehydration, immobility, low-fibre diet, hypothyroidism, hypercalcaemia, Parkinson's, constipating medications (iron, antimuscarinics).

3 · PR examination

Is there hard stool in the rectum (impaction)? Or is the rectum empty (high impaction / slow transit)? Guides management completely.

4 · If impacted — disimpaction

Movicol 8 sachets/day in 1L water for up to 3 days.

No response: phosphate enema PR.

Manual evacuation only if all else fails.

5 · If not impacted — laxative ladder

First: senna 2 tabs nocte (stimulant).

Add Movicol 1–2 sachets daily if inadequate.

Escalate: senna 4 tabs + Movicol 2 sachets BD.

6 · Opioid-induced: senna from day 1

Always co-prescribe senna when starting opioids. Osmotic laxatives alone are insufficient — you need a stimulant for opioid-induced constipation.

Drugs

Drug	Dose	Route	Notes
Senna	2 tabs (15mg)	PO nocte	Stimulant laxative. Increase to 4 tabs if insufficient. First-line for opioid-induced constipation.
Movicol (macrogol)	1–2 sachets	PO BD	Osmotic. Well tolerated. Disimpaction: 8 sachets/day in 1L water.
Bisacodyl suppository	10mg	PR	When oral laxatives insufficient or rectal loading present.
Phosphate enema	1 enema	PR	Rectal impaction not clearing with oral agents.

Red flags

Abdominal distension + vomiting + no flatus — obstruction until proven otherwise, do NOT give laxatives
Blood PR in new-onset constipation — needs colonoscopy/CT investigation
Constipation with hypercalcaemia on bloods — treat the hypercalcaemia
No response to disimpaction after 3 days — review, AXR, consider colorectal referral

Reference: BNF / NICE CG151 (Opioids in Palliative Care) / NICE Constipation CKS