Opioid Analgesic — Severe Ureteric Colic / Post-Operative Pain Pregnancy: Use with caution; neonatal respiratory depression if given near delivery; withdrawal in neonate

Morphine

Brand names: Oramorph, Morphine Sulfate, MST Continus

Adult dose

Dose: 2.5-10 mg IV/IM titrated; 10-30 mg oral every 4-6 hours

Route: Intravenous / Intramuscular / Subcutaneous / Oral

Frequency: IV: titrate in 2.5 mg increments every 5 minutes; Oral: every 4-6 hours

Max: Titrated to pain relief

Second-line to NSAIDs for ureteric colic. First-line for post-TURBT, post-nephrectomy, and major urological surgery. PCA (patient-controlled analgesia) commonly used post-major surgery

Paediatric dose

Dose: 0.05-0.1 mg/kg IV (acute pain); 0.2-0.5 mg/kg oral mg/kg

Route: IV / Oral

Frequency: Every 4-6 hours as required (oral); IV: titrate to effect

Max: 0.1 mg/kg per IV dose

Child 1-5 years: 1-2.5 mg oral/SC. Child 6-11 years: 2.5-5 mg. Child 12 years and over: 5-10 mg. Neonates and infants under 1 year: seek specialist opinion — respiratory depression risk

Dose adjustments

Renal

Significant caution in renal impairment — active metabolite (morphine-6-glucuronide, M6G) accumulates causing prolonged respiratory depression; reduce dose and extend interval; avoid in eGFR under 10

Hepatic

Reduce dose in hepatic impairment; avoid in severe liver disease

Paediatric weight-based calculator

Patient weight (kg)

Child 1-5 years: 1-2.5 mg oral/SC. Child 6-11 years: 2.5-5 mg. Child 12 years and over: 5-10 mg. Neonates and infants under 1 year: seek specialist opinion — respiratory depression risk

Clinical pearls

Antidote: naloxone (400 micrograms IV/IM/intranasal; repeat every 2-3 minutes; infusion if prolonged effect) — duration shorter than morphine, repeat dosing required
Active metabolite M6G: accumulates in renal impairment causing prolonged and unpredictable respiratory depression — oxycodone or fentanyl preferred in patients with significant CKD
Opioids for renal colic: effective but cause nausea and sedation that NSAIDs avoid; use as second-line if NSAIDs contraindicated
Post-urological surgery: morphine PCA is standard for major procedures (nephrectomy, cystectomy, prostatectomy); small regular SC doses for less major procedures
Controlled Drug Schedule 2 in UK — full CD prescription requirements; stock counted daily in hospitals

Contraindications

Acute respiratory depression
Paralytic ileus
Head injury with raised intracranial pressure (relative — blunts neurological assessment)
Concurrent MAOI use (within 14 days)

Side effects

Respiratory depression (most serious)
Nausea and vomiting
Constipation
Sedation
Pruritus
Urinary retention
Hypotension
Dependence

Interactions

CNS depressants (additive respiratory depression)
MAOIs (serotonin syndrome, opioid toxicity)
Gabapentin / pregabalin (MHRA 2017 — additive respiratory depression)
Naltrexone (precipitates withdrawal)

Monitoring

Respiratory rate and SpO2 (continuous with IV titration)
Sedation score
Pain scores (NRS)
Bowel function
Urinary retention

Reference: BNFc; BNF 90; RCEM Clinical Standards for Emergency Analgesia; EAU Urolithiasis Guidelines 2024; BNFc. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways