Pharmacology · patient case question
What is the mechanism of action of naloxone?
Patient case: Reviewing a long medication list
Patient: Female, 55 years old
Chief Complaint: Presents for a comprehensive examination.
Background: Graves disease, hypertension, asthma. She carries a naloxone kit because a family member has opioid use disorder.
Medications: Propylthiouracil · lisinopril · albuterol inhaler · naloxone (rescue kit)
Vital Signs: BP 132/84 mmHg · HR 84 bpm · RR 16
Show answer and explanation
Correct answer: D. Competitive antagonist at the mu opioid receptor
- A. Buprenorphine is the mu partial agonist; nalbuphine and butorphanol are agonist-antagonists. Naloxone has no agonist activity at all.
- B. Benzodiazepine receptor antagonism is FLUMAZENIL — the reversal agent for midazolam and diazepam. Confusing the two reversal agents is a classic exam trap.
- C. Monoamine reuptake inhibition describes the SNRI antidepressants, unrelated to opioid reversal.
- D. CORRECT. Naloxone is a pure COMPETITIVE ANTAGONIST with high affinity for the mu opioid receptor. It displaces the agonist and reverses respiratory depression within minutes. The critical clinical caveat: naloxone's duration of action (roughly 30 to 90 minutes) is SHORTER than that of many opioids, so re-narcotisation can follow and the patient must be observed or transported.