Naloxone is a potent, competitive opioid receptor antagonist. In the 20mcg strength, it is primarily used as an adjunct in spinal or epidural anesthesia to mitigate opioid-induced side effects like pruritus and nausea, without reversing analgesia. It is a pure antagonist with no agonist activity, high affinity for mu-opioid receptors, and rapid onset of action.
Adult: For opioid-induced pruritus/nausea in neuraxial anesthesia: 20-40 mcg (0.02-0.04 mg) IV bolus, repeated as needed. Often administered as a continuous infusion of 1-5 mcg/kg/hr. Maximum single dose for this indication is typically 100 mcg.
Note: For 20mcg dose: Usually drawn from a 400mcg/mL or 1mg/mL ampoule and diluted. Administer IV slowly over 30-60 seconds. For epidural use, must be preservative-free. Continuous ECG, BP, and respiratory monitoring required. Have resuscitation equipment available.
Naloxone competitively binds to opioid receptors (mu, kappa, delta) with high affinity, displacing opioid agonists and reversing or blocking their effects. At the 20mcg dose used in anesthesia, it preferentially antagonizes undesirable side effects (pruritus, nausea) mediated via mu-opioid receptors in the chemoreceptor trigger zone and spinal cord, while preserving supraspinal analgesia.
Pregnancy: Category B: Animal studies show no risk, but no adequate human studies. Use only if clearly needed. May precipitate withdrawal in fetus of opioid-dependent mother.
Driving: Naloxone reverses opioid sedation. However, patients should not drive or operate machinery until fully recovered from the effects of both the opioid and naloxone, and any underlying condition.
| Opioid Agonists (Morphine, Fentanyl, Pethidine) | Naloxone reverses analgesic and adverse effects. May precipitate withdrawal in dependent patients. | Major |
| Opioid Partial Agonists (Buprenorphine) | May be difficult to fully reverse effects due to high receptor affinity of buprenorphine. Larger/ repeated doses may be needed. | Major |
| Clonidine | Naloxone may reverse the hypotensive effects of clonidine. | Moderate |
| Cardiotoxic Drugs (e.g., Halothane) | Increased risk of ventricular arrhythmias. | Moderate |