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Non-Opioid Analgesic / Antipyretic — IV Pregnancy: Safe in pregnancy at standard doses

Paracetamol (IV)

Brand names: Perfalgan

Adult dose

Dose: 1 g IV every 4-6 hours
Route: Intravenous infusion (over 15 minutes)
Frequency: Every 4-6 hours (maximum four doses in 24 hours)
Max: 4 g/day (3 g/day in patients over 50 kg with hepatic impairment risk)
IV route reserved for when oral/PR route not possible. Equivalent analgesic and antipyretic efficacy to oral paracetamol once systemic levels equilibrate (approximately 1 hour). Available as 500 mg/50 mL and 1 g/100 mL

Paediatric dose

Dose: 15 mg/kg IV every 4-6 hours mg/kg
Route: IV infusion (over 15 minutes)
Frequency: Every 4-6 hours
Max: 60 mg/kg/day (max 3 g/day if under 33 kg; 4 g/day if over 33 kg)
Neonate 28-32 weeks gestational age: 7.5 mg/kg every 8-12 hours. Term neonate: 10 mg/kg every 4-6 hours

Dose adjustments

Renal

No dose reduction required; increase interval to 6 hours if eGFR under 30

Hepatic

Use with caution; reduce maximum daily dose to 2-3 g/day in severe hepatic impairment or chronic alcohol use

Paediatric weight-based calculator

Neonate 28-32 weeks gestational age: 7.5 mg/kg every 8-12 hours. Term neonate: 10 mg/kg every 4-6 hours

Clinical pearls

  • IV paracetamol: pharmacokinetically equivalent to oral once distributed; the key advantages are reliable delivery when gut unavailable (ileus, dysphagia, post-op) and more precise dosing timing
  • Antidote for overdose: N-acetylcysteine IV — Rumack-Matthew nomogram guides decision to treat; treatment within 8-10 hours prevents most hepatotoxicity
  • Enhanced recovery: regular paracetamol is the foundation of multimodal analgesia in ERAS protocols — scheduled every 6 hours, not PRN, to maintain steady-state levels
  • Hypotension with rapid infusion: infuse over exactly 15 minutes — faster administration causes transient hypotension due to vasodilation
  • Cost vs benefit: IV paracetamol significantly more expensive than oral; switch to oral or PR route as soon as swallowing is possible

Contraindications

  • Hepatic failure
  • Hypersensitivity to paracetamol

Side effects

  • Hepatotoxicity (overdose — N-acetylcysteine is antidote)
  • Hypotension (rapid IV infusion)
  • Rarely: thrombocytopenia, leucopenia

Interactions

  • Warfarin (enhanced anticoagulant effect — monitor INR with regular paracetamol use above 2 g/day)
  • Isoniazid, carbamazepine, alcohol (increase hepatotoxicity risk)
  • Cholestyramine (reduces absorption — IV route avoids this)

Monitoring

  • Pain scores and temperature
  • Liver function (if prolonged use at maximum dose)
  • Blood pressure during infusion

Reference: BNFc; BNF 90; Perfalgan SPC; PROSPECT Guidelines; ERAS Society Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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