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Opioid Receptor Antagonist Pregnancy: Safe in pregnancy for reversal of life-threatening opioid depression — maternal benefit outweighs fetal risk; may precipitate fetal withdrawal in opioid-dependent mothers (acceptable if maternal life at risk)

Naloxone (Intravenous — Opioid Reversal)

Brand names: Narcan

Adult dose

Dose: Respiratory depression: 100–200 mcg IV every 2–3 minutes until adequate respiration; post-op: 25–100 mcg IV titrated; opioid overdose: 400 mcg–2 mg IV, repeat every 2–3 minutes (may need up to 10 mg total in some cases)
Route: Intravenous (also IM, SC, intranasal)
Frequency: Every 2–3 minutes (titrated to effect)
Max: 10 mg in acute overdose (if no response to 10 mg, reconsider diagnosis)
Short duration of action (30–90 min) — re-narcotisation common with long-acting opioids; may need naloxone infusion (two-thirds of reversal dose per hour IV) to maintain reversal; IM preferred in community setting (Prenoxad autoinjector)

Paediatric dose

Dose: 10 mcg/kg IV every 2–3 minutes; for neonatal opioid depression: 10 mcg/kg IV/IM/ETT mcg/kg
Route: Intravenous
Frequency: Every 2–3 minutes to effect
Max: 2 mg total in paediatrics
Neonatal resuscitation: give to neonate only if mother received opioid within 4 hours — do NOT give if mother is opioid-dependent (neonatal withdrawal); BNFc

Dose adjustments

Renal

No dose adjustment required

Hepatic

No dose adjustment required

Paediatric weight-based calculator

Neonatal resuscitation: give to neonate only if mother received opioid within 4 hours — do NOT give if mother is opioid-dependent (neonatal withdrawal); BNFc

Clinical pearls

  • Titration is key in post-operative reversal: goal is adequate ventilation (RR >10, SpO2 >95%), NOT full reversal of all opioid effects — aggressive reversal causes acute pain recurrence and sympathetic surge; use 25-50 mcg IV increments in post-operative context
  • Re-narcotisation danger: heroin (diamorphine) has similar duration to naloxone; fentanyl, oxycodone, morphine, and especially methadone outlast naloxone — patients must be monitored for re-sedation; naloxone infusion at ~2/3 of effective reversal dose per hour prevents relapse
  • Buprenorphine overdose: buprenorphine has extremely high μ-receptor affinity — requires much higher naloxone doses (may need 4-8 mg or more); not fully reversible; supportive care with airway management may be more effective than high-dose naloxone
  • Pulmonary oedema: rapid opioid reversal causes acute catecholamine surge (sympathetic storm) — flash pulmonary oedema reported; titrate carefully rather than giving large boluses; particularly risky in patients with pre-existing cardiac disease
  • Prenoxad IM autoinjector: licensed for community use by non-medically trained bystanders (naloxone 1 mg/mL, 0.4 mg IM) — UK national take-home naloxone programme for people at risk of opioid overdose; intranasal naloxone (Nyxoid) also available

Contraindications

  • Physical opioid dependence without ability to monitor withdrawal (precipitates severe withdrawal)
  • Relative: mixed opioid-benzodiazepine overdose where opioid sedation is protective

Side effects

  • Acute opioid withdrawal (agitation, vomiting, tachycardia, hypertension, seizures in dependent patients)
  • Pulmonary oedema (post-reversal — catecholamine surge)
  • Cardiac arrhythmias (post-reversal catecholamine surge)
  • Pain recurrence (reversal of opioid analgesia in post-operative patients — titrate carefully)

Interactions

  • Buprenorphine — partial agonist; requires higher naloxone doses (buprenorphine's high receptor affinity difficult to overcome); may not fully reverse
  • Methadone — very long-acting; infusion required after reversal dose

Monitoring

  • Respiratory rate and SpO2 (continuous)
  • Consciousness level (GCS)
  • ECG (post-reversal arrhythmias)
  • Re-sedation surveillance (duration per opioid used)
  • Blood pressure (sympathetic surge)

Reference: BNFc; BNF 90; BNFc; MHRA SPC Narcan/Prenoxad; TOXBASE NPIS; PHE Take-Home Naloxone Programme; AAGBI Opioid Reversal 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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