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Opioid Receptor Antagonist

Naloxone (Intravenous — Opioid Reversal)

Brand names: Narcan

Used in: Poisoning & Overdose

Naloxone is a competitive opioid antagonist used to reverse opioid-induced respiratory depression and excessive sedation, by any of the intravenous, intramuscular or intranasal routes.

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.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION Important Dosage and Administration Instructions Pentazocine and Naloxone Tablets should be prescribed only by healthcare professionals who are knowledgeable about the use of opioids and how to mitigate the associated risks. Use the lowest effective dosage for the shortest duration of time consistent with individual patient treatment goals [see Warnings and Precautions ] . Reserve titration to higher doses of Pentazocine and Naloxone Tablets for patients in whom lower doses are insufficiently effective and in whom the expected benefits of using a higher dose opioid clearly outweigh the substantial risks. Many acute pain conditions (e.g., the pain that occurs with a …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-08-28. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

It competitively displaces opioids from mu (and other) opioid receptors, rapidly reversing respiratory depression, sedation and analgesia.

Prescribing in practice

  • Its duration of action is shorter than that of many opioids, so respiratory depression can recur (re-narcotisation) — keep the patient observed and be prepared to give repeat doses or start an infusion.
  • Titrate to adequate spontaneous breathing rather than full consciousness, to avoid precipitating acute withdrawal, agitation, pain and sympathetic surge, particularly in opioid dependence.
  • Long-acting or modified-release opioids and methadone require prolonged observation and often an infusion because a single dose is insufficient.

Monitoring

Monitor respiratory rate, oxygen saturation, conscious level and pain continuously, and observe for a prolonged period after the last dose because of the risk of recurrent respiratory depression.

Counselling the patient

  • Brief the team that reversal may be temporary and that the patient must be watched for return of sedation and respiratory depression.
  • Warn that abrupt full reversal can cause acute withdrawal, agitation and uncontrolled pain.
  • Follow Toxbase/NPIS advice in overdose, including when an infusion is indicated.

Evidence & guidelines

Recommended for opioid-induced respiratory depression (Resuscitation Council UK; Toxbase/NPIS).

Reference: MHRA SPC Narcan/Prenoxad; TOXBASE NPIS; PHE Take-Home Naloxone Programme; AAGBI Opioid Reversal Guidelines; 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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