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Inhalational Analgesic

Nitrous Oxide (Entonox)

Brand names: Entonox, Nitronox

Nitrous oxide as Entonox is a premixed fifty-fifty nitrous oxide and oxygen gas used for short-term inhaled analgesia during painful procedures such as fracture manipulation and dressing changes.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

Inhaled nitrous oxide produces rapid, short-lived analgesia and mild sedation through central effects including modulation of NMDA and opioid pathways, with quick onset and offset due to its low solubility.

Prescribing in practice

  • Contraindicated where trapped gas could expand, including pneumothorax, bowel obstruction and recent diving, as nitrous oxide diffuses into air-filled spaces.
  • Ensure adequate room ventilation or scavenging to limit occupational exposure for staff.
  • Prolonged or repeated exposure can inactivate vitamin B12 and cause megaloblastic anaemia and neuropathy.

Monitoring

Observe conscious level and oxygenation during use, ensuring the patient self-administers and remains rousable.

Counselling the patient

  • Breathe the gas yourself through the mouthpiece as the pain builds for best effect.
  • You may feel light-headed or tingly; this passes quickly once you stop.
  • Tell the team if you feel sick or very drowsy.

Evidence & guidelines

Entonox is an established option for procedural analgesia in UK emergency and trauma settings, valued for its rapid onset and offset.

Reference: BOC Entonox Product Information; MHRA Guidance on Entonox; SIGN 106; Rosen's Emergency Medicine 9th Ed; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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