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Opioid Analgesic — Modified-Release Oral Pregnancy: Use with caution — neonatal opioid withdrawal syndrome; neonatal respiratory depression if used near term; have naloxone available for neonate.

Morphine Slow-Release (Elderly Chronic Pain)

Brand names: MST Continus, Zomorph, MXL

Adult dose

Dose: Starting dose in opioid-naive elderly: 5–10 mg SR twice daily (MST) or 10–30 mg SR once daily (MXL); titrate every 24–48 hours based on breakthrough requirements; normal release (Oramorph/Sevredol) for titration and breakthrough
Route: Oral (swallow whole — do NOT crush SR formulations)
Frequency: Twice daily (MST 12h) or once daily (MXL 24h)
Max: No absolute maximum — titrate to pain control. High doses (>120 mg/day) require specialist review in elderly.
Geriatric dose principle: 'start low, go slow'. Elderly require 33–50% lower starting doses than adults due to reduced hepatic clearance, reduced renal clearance of active metabolite M6G, higher fat-to-muscle ratio (prolonged half-life), and increased CNS sensitivity. Must prescribe prophylactic laxative concurrently — constipation universal.

Paediatric dose

Dose: 0.2–0.5 mg/kg
Route: Oral
Frequency: Every 12 hours (SR formulation)
Max: As per specialist palliative/pain guidance
Paediatric SR morphine: 0.2–0.5 mg/kg every 12 hours for chronic cancer pain — specialist palliative care teams only. BNFc guidance.

Dose adjustments

Renal

AVOID in eGFR <30 mL/min — morphine-6-glucuronide (M6G) accumulates causing prolonged respiratory depression. Use fentanyl transdermal or oxycodone (with caution) in significant renal failure.

Hepatic

Reduce starting dose by 50% in significant hepatic impairment — prolonged half-life due to reduced first-pass metabolism. Monitor closely.

Paediatric weight-based calculator

Paediatric SR morphine: 0.2–0.5 mg/kg every 12 hours for chronic cancer pain — specialist palliative care teams only. BNFc guidance.

Clinical pearls

  • M6G accumulation in renal failure: morphine-6-glucuronide is the active opioid metabolite with 4–6× higher potency than morphine at mu-receptors; renally cleared; accumulates dramatically in CKD — causing prolonged respiratory depression hours after the last dose. A common cause of preventable opioid mortality in elderly with CKD. Use fentanyl transdermal patch as the safe alternative (inactive metabolites)
  • Breakthrough dose calculation: breakthrough morphine = 1/6th of total 24-hour SR morphine dose as immediate-release preparation (Oramorph/Sevredol); if ≥3 breakthrough doses required in 24 hours, increase the SR dose by that amount the next day
  • Opioid-induced constipation (OIC): naloxegol (Moventig) 25 mg once daily or methylnaltrexone SC are peripherally-acting mu-opioid receptor antagonists — treat OIC without reversing analgesia; licensed for adult patients who have failed regular laxatives. Prescribe stimulant laxative (senna) from day 1 of opioid initiation — do not wait for constipation to develop

Contraindications

  • eGFR <30 mL/min (M6G accumulation risk — use fentanyl patch instead)
  • Acute respiratory depression
  • Acute abdomen (may mask symptoms; relative)
  • Concurrent MAOIs (within 14 days — hypertensive crisis/serotonin syndrome)
  • Raised intracranial pressure (caution — CO2 retention)

Side effects

  • Constipation (universal — always co-prescribe laxative: macrogol or senna)
  • Nausea and vomiting (particularly on initiation — prescribe antiemetic PRN)
  • Sedation and cognitive impairment (heightened sensitivity in elderly)
  • Respiratory depression (principal life-threatening risk — antidote: naloxone)
  • Urinary retention (particularly in men with BPH)
  • Pruritus (histamine release)
  • Falls risk (sedation, dizziness, orthostatic hypotension in elderly)

Interactions

  • Benzodiazepines, gabapentinoids, alcohol (additive CNS/respiratory depression — MHRA 2020 black box warning)
  • MAOIs (MHRA absolute contraindication — excitatory or depressant crisis)
  • CYP3A4 inhibitors (erythromycin, ketoconazole — increase morphine levels)

Monitoring

  • Pain scores (NRS/VAS) at each review
  • Respiratory rate and SpO2 (respiratory depression risk)
  • Sedation score (and cognitive function in elderly)
  • Bowel function (constipation — laxative adequacy)
  • Renal function (eGFR) — M6G accumulation risk; avoid if eGFR <30
  • Falls assessment
  • Breakthrough dose usage (titration guide)

Reference: BNFc; BNF 90; NICE NG215 (Chronic Pain); SIGN 106 (Cancer Pain); BNFc; MHRA Drug Safety Update 2020 (opioid + CNS depressants); Palliative Care Formulary 6th Edition. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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