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Strong Opioid Analgesic Pregnancy: Compatible for acute severe pain; neonatal respiratory depression and withdrawal with prolonged use

Morphine (IV/IM — Anaesthesia/ICU)

Brand names: Morphine Sulfate (generic), Sevredol (oral), Oramorph (oral)

Adult dose

Dose: IV titration: 1–3 mg IV every 5 min to pain relief (total: 0.1–0.2 mg/kg). PCA: 1–1.5 mg bolus, 5-min lockout. ICU infusion: 2–4 mg/h. IM: 10 mg (morphine sulphate) every 4 hours PRN.
Route: IV (slow), IM, or oral
Frequency: Every 4 hours (regular); PCA on demand; infusion continuously
Max: Titrate to effect — no absolute maximum in palliative care; 10–15 mg/4h typical for moderate pain
Gold standard opioid analgesic. Active metabolite morphine-6-glucuronide (M6G) accumulates in renal failure — causes prolonged respiratory depression. Use with caution in renal failure.

Paediatric dose

Dose: 0.05 mg/kg
Route: IV slow bolus or IM
Frequency: Every 4–6 hours PRN or continuous infusion
Max: 0.1 mg/kg per dose
Concentration: 1 mg/mL (diluted for paediatrics) mg/ml
Neonates: 0.025–0.05 mg/kg IV (increased sensitivity to respiratory depression). Ensure naloxone is available. Infusion for neonates: 5–20 mcg/kg/h.

Dose adjustments

Renal

Significant caution: M6G accumulates in renal failure — reduce dose and extend intervals (use 50% dose if eGFR 10–50; avoid if eGFR <10 or use alternative opioid)

Hepatic

Caution in hepatic impairment — reduced clearance; extend interval

Paediatric weight-based calculator

Neonates: 0.025–0.05 mg/kg IV (increased sensitivity to respiratory depression). Ensure naloxone is available. Infusion for neonates: 5–20 mcg/kg/h.

Clinical pearls

  • Pain scale: use NRS 0–10 to guide titration; reassess every 30 min after IV administration
  • M6G accumulation in renal failure: classic presentation is delayed/recurrent respiratory depression many hours after dose — use oxycodone or fentanyl instead in renal failure
  • PCA: reduces total opioid use vs PRN regime in most studies
  • Opioid conversion: morphine 10 mg IV = oxycodone 6.7 mg IV; morphine 30 mg oral = morphine 10 mg IV (approximately)

Contraindications

  • Respiratory depression without ventilatory support
  • Paralytic ileus
  • Acute abdomen (in some contexts)
  • Concurrent MAOI use

Side effects

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

Interactions

  • CNS depressants — additive respiratory depression
  • MAOIs — serotonin syndrome and opioid crisis
  • Gabapentinoids — respiratory depression (MHRA warning)
  • Cimetidine — increased morphine levels

Monitoring

  • Respiratory rate (min 12/min before each dose)
  • SpO2
  • Sedation score
  • Pain score
  • Nausea and vomiting
  • Bowel function

Reference: BNFc; BNF; RCoA Acute Pain Management Guidelines; Oxford Pain Group; MHRA on gabapentinoids + opioids. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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