Constipation and opioid bowel care

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Constipation is difficult or infrequent stool passage relative to the person's normal pattern, not simply absence of a daily bowel action. Ask about stool form, straining, pain, incomplete emptying, leakage, nausea, appetite and ability to reach the toilet. A person with low intake may pass stool less often without discomfort, while daily small liquid stool can conceal impaction.

Opioids cause persistent bowel dysfunction because tolerance to gastrointestinal mu-receptor effects develops poorly. Prevention starts with the opioid, commonly a stimulant to restore propulsive activity plus an osmotic medicine to retain water. Review after dose increase, route change and reduced intake. If the patient already has impaction, ordinary prophylaxis is insufficient and requires a clearance plan first.

Examination is purposeful. Inspect hydration and medication, palpate for distension, tenderness and masses and assess bowel sounds without treating them as definitive. Rectal examination can identify hard stool, soft loading, tumour, bleeding or an empty rectum and guides rectal treatment. Explain why it is needed, obtain consent, provide privacy and analgesia and reconsider in severe neutropenia, thrombocytopenia, fissure or recent pelvic treatment.

Match laxative to mechanism. Senna or bisacodyl stimulates motility; macrogol or lactulose softens by osmotic water retention. Suppository or enema acts distally. Bulk-forming agents need fluid and useful propulsion and are often unsuitable in frailty, obstruction risk or poor intake. Renal and cardiac disease can make dehydration or electrolyte shifts more consequential, so titrate from a defined stool target.

Impaction may need staged oral and rectal treatment. A product-defined high-dose macrogol regimen can clear proximal loading in a person who can drink and has no obstruction. Hard stool in the rectum may need glycerol, bisacodyl, a suitable enema or manual removal by an experienced clinician with analgesia. Phosphate enemas can disturb electrolytes and are hazardous in renal failure; local policy governs selection.

Peripherally acting mu-opioid receptor antagonists reverse bowel opioid effects without usually removing central analgesia. Naloxegol is an oral option after inadequate laxative response; methylnaltrexone is a specialist subcutaneous option. Both require exclusion of obstruction and gastrointestinal-wall vulnerability. Strong CYP3A interactions alter naloxegol exposure, and renal impairment requires dose review.

Near death, the goal is comfort rather than an arbitrary frequency. Continue prevention while oral intake and opioid use make it useful, simplify treatment when swallowing fails and treat painful rectal loading. Avoid repeated invasive rectal procedures in a comfortable unresponsive person without evidence of distress. Explain the plan to families so reduced intake is not answered by burdensome laxative escalation.

Key points

Ask every patient starting a strong opioid about baseline bowel pattern and prescribe constipation prevention immediately unless diarrhoea or obstruction makes it unsafe.
First-line opioid regimen usually combines a stimulant such as senna with an osmotic softener such as macrogol, individualised to intake and stool consistency.
Do not rely on docusate alone for established opioid dysmotility and avoid bulk-forming fibre when intake is poor, transit is slow or obstruction is possible.
Assessment covers last satisfactory stool, form, straining, incomplete emptying, flatus, pain, vomiting, overflow, medicines, intake, mobility and toilet access.
Examine abdomen and perform rectal examination with consent when impaction, outlet disease or distal obstruction will change care; first assess bleeding and infection risk.
Hard rectal stool requires a rectal or disimpaction plan; adding only more proximal oral laxative may worsen pain and overflow.
Suspected complete obstruction, perforation or severe colic means stop stimulant, bulk and rectal treatment until urgent assessment.
Consider naloxegol or another peripherally acting mu-opioid antagonist only for opioid-induced constipation inadequately controlled by conventional laxatives and after obstruction and interaction review.
The gold-standard bowel plan states prophylaxis, stool target, escalation steps, rectal branch, obstruction red flags and review after every opioid or route change.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Opioid-induced dysmotility

Peripheral mu-receptor activation reduces propulsive contractions, increases fluid absorption and raises sphincter tone throughout the gastrointestinal tract.

Medicine and metabolic contributors

Anticholinergics, ondansetron, iron, calcium, diuretics, hypercalcaemia, hypothyroidism and dehydration commonly slow bowel transit or harden stool.

Functional and dietary factors

Low intake, immobility, weak abdominal muscles, poor privacy, inaccessible toilets and dependence for care reduce effective defaecation.

Structural and neurological causes

Tumour, stricture, pelvic-floor dysfunction, autonomic neuropathy, spinal compression and anal pain can obstruct or impair evacuation.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Slow colonic transit
Prolonged mucosal contact permits greater water absorption, producing progressively dry stool that becomes harder for the colon to propel.
2
Reduced propulsive motility
Opioids suppress coordinated peristalsis while increasing non-propulsive bowel tone, delaying transit without reliable tolerance developing over time.
3
Outlet dysfunction
Pain, pelvic-floor dyssynergia, neurological loss or immobility prevents rectal evacuation even when proximal stool is soft.
4
Faecal impaction
Retained stool enlarges and compresses rectal or colonic wall, causing overflow, retention, ulceration and systemic distress.
5
Obstructive pressure
A mechanical blockage accumulates gas and fluid proximally, producing distension, colic, vomiting, impaired perfusion and perforation risk.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Slow-transit constipation

Infrequent hard stool, bloating and reduced urge with constipating medicines or immobility suggests impaired proximal propulsion.

Outlet dysfunction

Repeated straining, rectal pressure, incomplete evacuation and need for digital support suggests distal or pelvic-floor difficulty.

Faecal impaction

Overflow liquid stool, rectal pain, urinary retention, agitation and hard mass on examination indicates impacted faeces.

Opioid bowel dysfunction

Constipation with reflux, nausea, abdominal discomfort and incomplete evacuation beginning after opioid exposure supports persistent peripheral mu effects.

Mechanical obstructionRed flag

Colic, progressive distension, vomiting and obstipation with malignant or surgical history requires urgent imaging and treatment change.

Stercoral complicationRed flag

Sudden severe pain, bleeding, fever, peritonism or shock after prolonged loading suggests ulceration, ischaemia or perforation.

Red flags requiring action

Obstipation, colic, vomiting and marked distension suggests obstruction and makes bulk-forming, stimulant and high-volume oral regimens unsafe until assessed.
Peritonism, fever, shock or sudden severe pain suggests perforation, ischaemia or stercoral complication and needs emergency review.
Overflow diarrhoea does not exclude impaction; liquid stool can pass around a hard rectal mass.
New urinary retention, agitation, nausea, reflux or reduced oral absorption can be caused by faecal loading even without volunteered constipation.
Rectal examination or treatment may cause bleeding or infection in severe thrombocytopenia, neutropenia, anal disease or recent pelvic treatment and needs individual risk review.
Peripheral opioid antagonists are contraindicated or high risk in known or suspected mechanical obstruction because perforation can occur.
New saddle symptoms, leg weakness or sphincter dysfunction requires emergency spinal or cauda-equina assessment rather than laxative escalation.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line bowel and medicine historyFirst stepFirst line
Why
Establish usual pattern, last satisfactory stool, Bristol type, straining, overflow, flatus, pain, vomiting, intake, mobility and constipating exposure.
Interpretation and limitations
Distinguish prevention failure, impaction, outlet dysfunction, low intake and obstruction before selecting treatment intensity.
02
Abdominal examination
Why
Assess hydration, distension, focal tenderness, peritonism, hernia, palpable stool, mass, bladder and bowel sounds.
Interpretation and limitations
Peritonism or marked obstructive features stops routine laxative escalation and triggers urgent imaging and specialist review.
03
Digital rectal examination
Why
Identify hard or soft loading, bleeding, tumour, anal pathology, sphincter tone or an empty distal rectum when findings change treatment.
Interpretation and limitations
Hard stool supports softening or manual strategy; weigh consent, discomfort, neutropenia and thrombocytopenia before examination or rectal medicines.
04
Targeted blood tests
Why
Check renal function, calcium, thyroid, glucose and electrolytes when metabolic cause, dehydration or treatment toxicity is plausible.
Interpretation and limitations
Correct contributors and use kidney and electrolyte results to avoid phosphate, magnesium or high-volume regimens that add harm.
05
CT abdomen and pelvis
Why
Define transition point, tumour, volvulus, perforation, ischaemia, faecal loading or pseudo-obstruction when red flags or uncertainty exist.
Interpretation and limitations
CT is the reference structural test for suspected malignant obstruction and directs surgery, stent, decompression or medical care.
06
Therapeutic bowel record
Why
Track administered doses, stool time and form, pain, overflow, continence and adverse effects against the agreed target.
Interpretation and limitations
Response is the practical standard for titration; persistent symptoms after confirmed adherence require examination and diagnosis review.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Mechanical bowel obstruction

Colic, vomiting, distension, obstipation, hernia or malignant disease requires imaging before routine escalation of motility or stool volume.

Faecal impaction

Rectal pressure, overflow diarrhoea, urinary symptoms and hard stool on examination supports distal loading needing disimpaction.

Ileus

Diffuse distension, reduced bowel activity and systemic illness, electrolyte disturbance or medicine exposure suggests non-mechanical motility failure.

Spinal or cauda-equina disease

New constipation with urinary retention, saddle loss, weakness or back pain can reflect neurological sphincter dysfunction.

Low-output normal variation

Reduced food intake may decrease frequency without discomfort or hard stool, so treatment follows symptoms and baseline rather than a daily rule alone.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Opioid prophylaxisStart stimulant and softener togetherFirst stepA strong opioid is initiated or increased and no obstruction or diarrhoea contraindicates prophylaxis.

1Record baseline bowel pattern, renal and cardiac status, intake and existing constipating medicines and agree a comfortable stool target.
2EscalationStart formulary senna plus macrogol or another stimulant-osmotic combination and give written dose, hydration, escalation and red-flag advice.
3Review within days and after every opioid change, titrating individual components to stool form and frequency and checking adherence and toilet access.

02Suspected impactionLocate loading before clearing itOverflow, rectal pressure, urinary symptoms, prolonged absence of satisfactory stool or failed oral laxatives suggests impaction.

1Assess obstruction and perforation red flags, examine abdomen and perform consented rectal examination when safe and management-changing.
2Use oral macrogol for proximal loading if the person can drink and obstruction is excluded, and choose suppository, enema or manual disimpaction for distal stool based on consistency and risk.
3Provide analgesia and skin care, confirm clearance and then restart an effective preventive regimen rather than stopping all bowel treatment.

03Obstruction concernStop unsafe bowel stimulationColic, distension, vomiting, obstipation, peritonism or sudden severe pain develops.

1Withhold bulk, stimulant and rectal treatment, use ABCDE care and obtain urgent CT and surgical or oncology assessment within the treatment ceiling.
2Correct fluid and electrolyte compromise, provide non-oral analgesia and antiemetic and decompress when indicated.
3Choose surgical, stent, venting or medical obstruction care and reintroduce bowel treatment only if transit and the new plan safely permit it.

04Refractory opioid constipationConsider peripheral opioid antagonism safelyOpioid-induced constipation persists despite adherence to an adequate tolerated conventional laxative regimen.

1Reconfirm diagnosis, adherence, rectal loading and opioid necessity and exclude mechanical obstruction, acute abdomen and high perforation risk.
2Select naloxegol, methylnaltrexone or another local option through the BNF and formulary with renal, hepatic, CYP interaction and route review.
3Monitor prompt bowel response, cramping, diarrhoea, withdrawal or reduced analgesia and stop and investigate severe abdominal pain.

Key medicines and prescribing safety5 treatments · regimens, roles and cautions

Stimulates colonic propulsion and is commonly paired with an osmotic laxative to prevent or treat opioid bowel dysfunction.

Senna stimulant prophylaxis

Start 15 mg orally at night in many adults beginning strong opioid treatment, increasing to 30 mg at night or a local divided regimen according to stool response and the BNF.

Avoid during suspected complete obstruction, perforation or severe colic; cramping and diarrhoea require reduction and prolonged use still needs diagnosis review.

Retains water in stool and complements a stimulant for hard stool and opioid-associated slow transit.

Macrogol osmotic laxative

Use one compound macrogol sachet orally daily initially and titrate commonly to one to three sachets daily; use the product's separate impaction regimen only after obstruction exclusion and with adequate fluid and supervision.

Volume may be difficult in advanced illness; review fluid and electrolyte status, aspiration and obstruction and do not improvise high-dose regimens from maintenance instructions.

Stimulates colonic or rectal evacuation and can help a planned distal-loading regimen.

Bisacodyl for distal or oral stimulation

Give 5 to 10 mg orally at night when a stimulant is needed, or one 10 mg rectal suppository when distal treatment is indicated and rectal administration is safe.

Avoid in obstruction, acute abdomen and unsafe rectal conditions; cramps, diarrhoea and mucosal trauma occur and suppository response should be reviewed.

Antagonises peripheral gastrointestinal mu receptors while generally preserving central opioid analgesia.

Naloxegol for laxative-inadequate opioid constipation

Use 25 mg orally once daily when conventional laxatives are inadequate, reducing to 12.5 mg initially in moderate or severe renal impairment and following product interaction instructions.

Contraindicated in known or suspected obstruction or high perforation risk; strong CYP3A inhibitors are contraindicated and severe pain, diarrhoea or withdrawal requires urgent review.

Provides peripheral mu-receptor antagonism when an oral option is unsuitable or a rapid specialist response is required.

Methylnaltrexone under specialist selection

Use the weight-based subcutaneous product regimen for opioid-induced constipation when conventional laxatives are inadequate, with frequency and renal or hepatic adjustment verified in the current SmPC and local palliative pathway.

Exclude mechanical obstruction and gastrointestinal-wall compromise; severe abdominal pain may indicate perforation and rapid bowel action requires toileting and skin preparation.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Impaction and overflow

A hard stool mass obstructs evacuation while liquid leaks around it, leading carers to mistake the presentation for diarrhoea.

Urinary and delirium effects

Rectal loading compresses bladder outflow and creates pain, nausea and agitation, precipitating retention, infection and delirium.

Stercoral injury

Sustained pressure from hard stool causes mucosal ulceration, bleeding, ischaemia and perforation with life-threatening faecal peritonitis.

Oral-route failure

Nausea, reflux and vomiting prevent absorption of analgesic, antiseizure and other essential medicines and worsen dehydration.

Laxative harm

Overtreatment causes cramping, diarrhoea, dehydration, electrolyte loss, incontinence and skin damage, while bulk agents can worsen obstruction.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Record bowel action time, Bristol stool form, straining, incomplete emptying, overflow and pain against the individual target.
Review nausea, reflux, appetite, bladder symptoms, agitation and oral-medicine absorption as possible secondary constipation effects.
Check adherence, ability to drink macrogol, caregiver administration and physical toilet access before declaring pharmacological failure.
Repeat abdominal and rectal assessment when symptoms persist, overflow appears or the clinical pattern changes.
Monitor hydration, renal function and electrolytes during diarrhoea, high-dose osmotic treatment or frailty.
After peripheral opioid antagonism monitor cramping, diarrhoea, withdrawal, analgesia and severe abdominal pain.
Reconcile the bowel plan whenever opioid, antiemetic, anticholinergic, iron, calcium or care setting changes.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Overflow is still constipation

Liquid leakage around an impaction is easily mistaken for laxative excess and can worsen if all treatment is stopped.

Rectal examination changes treatment

Knowing whether distal stool is hard, soft or absent directs safer oral, suppository, enema or imaging choices.

Opioid tolerance spares the bowel

Analgesic sedation may improve with time while peripheral gastrointestinal effects often persist and still need prophylaxis.

Bulk requires propulsion

Fibre can increase stool volume and obstruction risk when fluid intake and motility are poor.

PAMORA is not first rescue

Peripheral antagonists follow adequate conventional laxatives and structural safety checks rather than replacing assessment.

Comfort defines frequency

A low-intake dying patient does not need invasive daily evacuation if there is no loading, pain or distress.

11Common pitfallsFrequent interpretation and management errors.

01
Starting a strong opioid without a bowel prescription and review plan.
02
Treating overflow diarrhoea as proof that impaction is absent.
03
Escalating oral laxative without examining suspected distal loading.
04
Giving bulk-forming fibre during poor intake or obstruction risk.
05
Using stimulant, enema or suppository in suspected perforation or complete obstruction.
06
Performing rectal procedures without consent or neutropenia and platelet review.
07
Using phosphate enema without renal and electrolyte risk assessment.
08
Starting naloxegol despite mechanical obstruction or strong CYP3A inhibition.
09
Stopping all prophylaxis immediately after successful disimpaction.
10
Pursuing an arbitrary daily stool in a comfortable person in the final hours.