A 42-year-old man with chronic pain from metastatic cancer is on morphine 60 mg/day. He presents to the emergency department with severe respiratory depression (RR 8/min), pinpoint pupils, and altered mental status. His wife reports he took an extra dose 2 hours ago. Arterial blood gas shows pH 7.20, PaCO₂ 85 mmHg, PaO₂ 55 mmHg. What is the immediate pharmacological intervention?

Explanation

## Opioid Overdose Management ### Clinical Presentation The patient exhibits the classic triad of opioid toxicity: - Respiratory depression (RR 8/min, severe hypoventilation) - Miosis (pinpoint pupils) - Altered consciousness Combined with severe respiratory acidosis (pH 7.20, PaCO₂ 85 mmHg) and hypoxemia (PaO₂ 55 mmHg), this is a life-threatening opioid overdose. ### Mechanism of Naloxone **Key Point:** Naloxone is a competitive, non-selective opioid antagonist that binds with high affinity to μ, δ, and κ receptors, displacing opioids and rapidly reversing their effects. Naloxone crosses the blood–brain barrier and reverses: 1. Respiratory depression → restores minute ventilation 2. Miosis → pupils dilate 3. CNS depression → restores consciousness ### Dosing & Administration **High-Yield:** Standard initial dose is **0.4–0.8 mg IV push**. Repeat every 2–3 minutes up to a cumulative dose of 10 mg if no response. IM or intranasal routes are acceptable if IV access unavailable. **Clinical Pearl:** Naloxone has a shorter half-life (~30–81 minutes) than most opioids (especially long-acting formulations like morphine). Redosing or continuous infusion may be required to prevent recurrence of respiratory depression. ### Why Other Options Are Wrong | Option | Reason | |--------|--------| | **Flumazenil** | Benzodiazepine antagonist; ineffective against opioids. Also contraindicated if benzodiazepines are co-ingested (risk of seizures). | | **Sodium bicarbonate** | Treats the *consequence* (acidosis) but not the *cause* (hypoventilation). Oxygenation and ventilation must be restored first. | | **Doxapram** | Respiratory stimulant with narrow margin of safety; not first-line. Naloxone is the definitive antidote. | ### Supportive Care **Warning:** Always ensure adequate oxygenation and ventilation (bag-mask ventilation or intubation if needed) *while* preparing naloxone. Do not delay airway management for medication administration. ### Post-Reversal Monitoring - Observe for at least 4–6 hours (or longer if long-acting opioid suspected) - Monitor for withdrawal symptoms (agitation, tachycardia, hypertension, diaphoresis) - Repeat naloxone doses or infusion if respiratory depression recurs [cite:Harrison 21e Ch 394]