Analgesic
Pregnancy: C — use at lowest effective dose; neonatal withdrawal risk with prolonged use
Morphine
Brand names: Oramorph, MST Continus, Morphgesic SR
Adult dose
Dose: 2.5–5mg IV (titrate to effect)
Route: IV / IM / SC
Frequency: Every 4h PRN; IV titrate every 5 min
Max: Titrate to effect — no fixed ceiling for acute pain
IV: give 2.5–5mg slowly over 5 min, reassess, repeat as needed. IM/SC: 5–10mg. Reduce by 50% in elderly or opioid-naive patients. Dose in mg/kg: 0.1mg/kg IV.
Paediatric dose
Dose: 0.1 mg/kg
Route: IV (slow over 5 min)
Frequency: Every 4h PRN
Max: 10mg
Concentration: 1 mg/ml
Dose adjustments
Renal
Reduce dose or avoid in CKD — active metabolites (M6G) accumulate. Use fentanyl or oxycodone if GFR <30.
Hepatic
Reduce dose in severe hepatic impairment.
Paediatric weight-based calculator
Clinical pearls
- Titrate IV morphine in small increments (2.5mg q5 min) — reassess pain and sedation after each dose.
- Always co-prescribe an antiemetic (cyclizine 50mg or ondansetron 4mg) and laxative.
- Naloxone duration (<45 min) is SHORTER than morphine — re-sedation risk with larger doses. May require infusion.
- In CKD3b–5 and dialysis patients: use oxycodone or fentanyl instead — morphine metabolites accumulate causing prolonged respiratory depression.
Contraindications
- Active respiratory depression
- Acute asthma attack
- Paralytic ileus
- MAO inhibitor use within 14 days
Side effects
- Nausea and vomiting — prescribe antiemetic prophylactically
- Constipation — prescribe laxative prophylactically
- Respiratory depression (dose-dependent)
- Pruritus (spinal/epidural route particularly)
- Urinary retention
- Sedation, hypotension
Interactions
- CNS depressants: additive sedation and respiratory depression
- MAOIs: potentially fatal — absolutely contraindicated
- Naloxone: reversal agent — 0.4mg IV, repeat every 2–3 min
- Rifampicin: reduces plasma morphine levels
Monitoring
- Respiratory rate
- sedation score (RASS or NRS)
- pain score (NRS)
- SpO₂
Reference: BNFc; NICE BNF 84; Scottish Palliative Care Guidelines 2024. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators
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