naloxone
opioid antagonist· Brands: Narcan, Prenoxad, Evzio, NyxoidIMINHIVSC
Mechanism of action
Naloxone is a competitive antagonist at mu, delta, and kappa opioid receptors. It has high affinity for these receptors but no intrinsic agonist activity, so it displaces opioid molecules and reverses opioid effects, including respiratory depression and analgesia, without producing any opioid-like response itself.
Pharmacokinetics
Naloxone undergoes rapid hepatic metabolism by conjugation to glucuronides. Its elimination half-life is approximately 1 hour, which is shorter than most opioids. It is well absorbed after parenteral administration but has poor oral bioavailability. Onset of action is rapid: 1 to 2 minutes after intravenous injection, and 3 to 5 minutes after subcutaneous or intramuscular administration. It crosses the placenta and is excreted in breast milk.
Indications & dosing
Acute opioid overdose
Titrate to response; consider intranasal or IM if IV access not available.
- adult · IV: 0.4–2 mg every 2-3 min · Titrate to response; consider intranasal or IM if IV access not available.
Acute opioid overdose
Titrate to response; may be used if IV access not available.
- adult · IM: 0.4–2 mg every 2-3 min · Titrate to response; may be used if IV access not available.
Acute opioid overdose
Max 2 mg per dose; repeat as needed.
- pediatric · IV: 0.1 mg/kg every 2-3 min · Max 2 mg per dose; repeat as needed.
Postoperative opioid-induced respiratory depression
Titrate to respiratory rate and depth; avoid full reversal to prevent pain or withdrawal.
- adult · IV: 0.1–0.2 mg every 2-3 min · Titrate to respiratory rate and depth; avoid full reversal to prevent pain or withdrawal.
Contraindications & precautions
- Known hypersensitivity to naloxone · No other absolute contraindications.
- Opioid dependence · Precipitates acute withdrawal syndrome.
- Cardiovascular disease · May cause hypertension and arrhythmias.
- Resuscitation facilities and trained staff must be available; repeat doses may be needed as naloxone has a short duration of action relative to many opioids.
- Use with caution in opioid-dependent patients; abrupt reversal may precipitate severe withdrawal.
- Monitor for resedation and respiratory depression after the initial response because naloxone effects may wear off before the opioid.
- Caution in patients with cardiovascular disease, as naloxone can cause hypertension and potentially life-threatening arrhythmias.
- In opioid overdose, aim to restore adequate ventilation rather than complete reversal to avoid withdrawal in dependent patients.
- Neonates of opioid-dependent mothers: naloxone may precipitate acute withdrawal; use with caution.
Adverse effects
- Nausea and vomiting
- Sweating
- Tachycardia
- Hypertension
- Agitation
- Acute withdrawal syndrome in opioid-dependent patientsserious
- Pulmonary edemaserious
- Cardiac arrestserious
Monitoring, pregnancy & toxicity
- Respiratory rate · After initial dose, then every 15-30 minutes until stable
- Level of consciousness · After initial dose, then every 15-30 minutes until stable
- Blood pressure and heart rate · Monitor for hypertension or tachycardia from withdrawal
- Signs of opioid withdrawal · Observe for agitation, nausea, vomiting, pain
- Pregnancy: Naloxone is recommended for opioid overdose in pregnancy; benefit outweighs risk. Use with caution as it may precipitate withdrawal in both mother and fetus, requiring close monitoring.
- Toxicity: Precipitated opioid withdrawal (agitation, hypertension, tachycardia, vomiting, pain, diarrhoea) · Supportive treatment, titrate naloxone to avoid severe withdrawal, monitor closely.
- Toxicity: Neonatal withdrawal syndrome after maternal use in late pregnancy · Supportive care in a neonatal unit; may require opioids to control withdrawal (e.g., morphine).
- Toxicity: Pulmonary oedema and cardiac arrest (rare) · Immediate supportive measures, including oxygen and fluid management; treat cause if identified.
Clinical notes
Naloxone is indicated for the emergency reversal of opioid-induced respiratory depression. Administer titrated doses to achieve adequate ventilation without precipitating severe withdrawal. The duration of action is shorter than that of many opioids, so repeated doses or a continuous infusion may be necessary. It is also used to support resuscitation in suspected opioid overdose. Naloxone can be given by intravenous, intramuscular, subcutaneous, or intranasal routes. Training in take-home naloxone is encouraged for people at risk, and doses are available in various formulations.
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BNF; local formulary