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Non-opioid Analgesic — Antipyretic Pregnancy: Safe at recommended doses — first-line analgesic in pregnancy at all trimesters

Paracetamol IV (Orthopaedic — Opioid-Sparing)

Brand names: Perfalgan

Adult dose

Dose: 1000 mg IV infusion over 15 minutes every 4–6 hours; 500 mg if weight <50 kg
Route: Intravenous
Frequency: Every 4–6 hours
Max: 4000 mg/day (4 g/day); 3000 mg/day if weight <50 kg, elderly, hepatic impairment, or chronic alcohol use
Give as 15-minute IV infusion. Maximum 4 doses in 24 hours. IV paracetamol achieves higher peak plasma levels than oral — equivalent analgesic efficacy. Transition to oral as soon as patient can tolerate to reduce cost and IV line complications.

Paediatric dose

Dose: 15 mg/kg
Route: Intravenous
Frequency: Every 4–6 hours
Max: 60 mg/kg/day (maximum 4 g/day in adolescents >50 kg)
Neonates and infants: reduced dosing schedule — see BNF for Children; 7.5 mg/kg every 4 hours for neonates

Dose adjustments

Renal

Use with caution in severe renal impairment (eGFR <30 mL/min); reduce frequency

Hepatic

Severe hepatic impairment: avoid or use with extreme caution; max 3 g/day if mild-moderate impairment

Paediatric weight-based calculator

Neonates and infants: reduced dosing schedule — see BNF for Children; 7.5 mg/kg every 4 hours for neonates

Clinical pearls

  • IV paracetamol vs oral: peak plasma levels are similar; IV is not significantly more effective than oral when equivalent doses are given to patients with intact GI function — transition to oral as soon as possible to reduce cost (IV paracetamol is ~40× more expensive than oral)
  • ERAS protocols: regular scheduled paracetamol (oral or IV) combined with NSAID is the multimodal analgesic backbone reducing opioid consumption by 20–30% post-arthroplasty
  • Paracetamol overdose: 10–15 g in adults causes hepatic necrosis; NAC (N-acetylcysteine) is the antidote — most effective within 8 hours; nomogram (Rumack-Matthew) guides treatment
  • MHRA: Fixed-dose combination products (co-codamol, co-dydramol) carry paracetamol — patients may inadvertently exceed 4 g/day if also taking paracetamol separately; counsel carefully
  • Weight <50 kg: dose at 500 mg (not 1000 mg) — risk of hepatotoxicity at full dose in low body weight patients

Contraindications

  • Severe hepatic impairment
  • Hypersensitivity to paracetamol

Side effects

  • Hepatotoxicity — dose-dependent; MHRA: overdose is leading cause of acute liver failure in UK
  • Hypotension (with IV infusion — rare)
  • Thrombocytopenia (rare)
  • Skin reactions (rare)

Interactions

  • Warfarin — regular paracetamol (>4 doses/week) modestly increases INR; intermittent use generally safe
  • Alcohol (chronic) — depletes glutathione stores; hepatotoxicity risk at lower doses; limit to 3 g/day
  • Cholestyramine — reduces paracetamol absorption (separate by 1 hour)

Monitoring

  • Liver function if prolonged use or pre-existing hepatic disease
  • Total daily paracetamol intake across all preparations
  • Body weight (for dosing) in patients <50 kg

Reference: BNFc; BNF 90; NICE NG124 (Hip Fracture); ERAS Society Orthopaedic Guidelines; Perfalgan SPC; MHRA Paracetamol Overdose Guidance. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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