Opioid Analgesic — Patient-Controlled Analgesia Pregnancy: Caution — neonatal respiratory depression and withdrawal

Morphine (PCA — Post-Operative Pain)

Brand names: Morphine Sulfate

Adult dose

Dose: PCA: bolus 1–1.5 mg, lockout 5 min, max 6 doses/h. Background infusion: usually NOT recommended for opioid-naïve patients (risk of respiratory depression). IV bolus titration: 2–3 mg every 5–10 min until pain controlled.

Route: IV (PCA pump or nurse-controlled)

Frequency: On demand (PCA) or scheduled

Max: Titrate to pain response — no absolute maximum

PCA reduces total opioid use vs PRN IM regime. No routine background infusion for opioid-naïve patients. Naloxone and oxygen should be immediately available. Opioid-tolerant patients may require higher bolus or background infusion.

Paediatric dose

Dose: 0.025 mg/kg

Route: IV (bolus or NCA — nurse-controlled)

Frequency: Every 5–10 min PRN (PCA in children ≥6 years); NCA in younger children

Max: 0.05 mg/kg per bolus (max 2.5 mg)

Concentration: 1 mg/mL mg/ml

PCA in children: suitable from age ~6 years and above who can understand the concept. NCA (parent/nurse-controlled) in younger children — same dosing but administered by caregiver.

Dose adjustments

Renal

M6G accumulates — reduce dose, extend intervals; monitor closely for delayed respiratory depression

Hepatic

Reduce dose in hepatic impairment

Paediatric weight-based calculator

Patient weight (kg)

PCA in children: suitable from age ~6 years and above who can understand the concept. NCA (parent/nurse-controlled) in younger children — same dosing but administered by caregiver.

Clinical pearls

PCA vs IM opioid: patients control their own analgesia — better pain scores, no nurse delay, reduces total opioid
No background infusion for opioid-naïve: ANZCA guidelines — background infusions in opioid-naïve patients on PCA increase respiratory adverse events without improving analgesia
Pruritus from epidural/intrathecal morphine: ondansetron 4 mg IV or nalbuphine 3–5 mg IV may help
Always prescribe antiemetic (e.g., cyclizine/ondansetron) alongside PCA prescription

Contraindications

Respiratory depression
Unmonitored ward setting without adequate nursing
Severe raised ICP

Side effects

Respiratory depression
Nausea/vomiting (antiemetic co-prescription mandatory)
Pruritus (especially intrathecal/epidural morphine)
Constipation
Urinary retention
Sedation

Interactions

CNS depressants — respiratory depression
Gabapentinoids — MHRA warning re: respiratory depression

Monitoring

Respiratory rate (≥12/min before each bolus)
Sedation score (Richmond RASS or Pasero Opioid-Induced Sedation Scale)
Pain score
Nausea
Urine output

Reference: BNFc; BNF; ANZCA Acute Pain Management Guidelines; RCoA Acute Pain Handbook. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways