Pharm 101: Naloxone

Class

Opioid antagonist

Pharmacodynamics

• Pure opioid antagonist that binds to mu-opioid binding sites
• Very high affinity for mu receptors, lower affinity for other receptor binding sites
• No tolerance to antagonist action

Pharmacokinetics

• IV administration:
  • Reverses opioid toxicity in 1-3 minutes
  • Duration of action 1-2 hours
• Rapid first pass metabolism

Clinical uses

• Life-threatening respiratory and CNS depression in opioid toxicity:
  • Initial dose 0.1-0.4 mg
  • Maintenance dose 0.4-0.8 mg, repeated as necessary
• Withdrawal after chronic administration does not precipitate an abstinence syndrome

Adverse effects

• Opioid withdrawal: precipitates abstinence syndrome in dependent users
• Resedation (short duration of action)
  • Severely depressed patient may recover after a single dose and appear normal, and then relapse into coma after 1-2 hours
• Ways to avoid: smaller/titrated doses, infusion, route of administration

References

• Katzung BG. Basic and Clinical Pharmacology. 14e. 2018: 570-572