A 65-year-old woman with severe postoperative pain 6 hours after abdominal surgery has nausea and is unable to take oral medications. She has no prior opioid exposure. Which opioid is the drug of choice for acute postoperative analgesia in this patient?

Explanation

## Acute Postoperative Opioid Analgesia in Opioid-Naïve Patients **Key Point:** Morphine (IV or IM) is the gold-standard first-line opioid for acute postoperative pain in opioid-naïve patients, especially when oral intake is not possible. ### Why Morphine for Acute Postoperative Pain? 1. **Rapid onset** — IV onset 5–10 min; IM onset 15–30 min 2. **Titratable** — IV route allows rapid dose adjustment to effect 3. **Parenteral formulation** — ideal when patient cannot take oral medications 4. **Predictable kinetics** — short half-life (~2–3 hrs), no accumulation with single doses 5. **Reversible** — naloxone antagonism available if needed 6. **Proven safety** — extensive perioperative experience ### Acute vs. Chronic Pain Management **High-Yield:** In acute postoperative settings, morphine is preferred over extended-release formulations or long-acting agents (fentanyl patches, methadone) because: - Pain intensity and duration are unpredictable - Rapid titration is essential - Risk of overdose from fixed-dose, long-acting drugs is high ### Comparison with Alternatives | Opioid | Route | Onset | Use in Acute Postop | Reason for Avoidance | |--------|-------|-------|---------------------|----------------------| | **Morphine** | IV/IM/PO | 5–30 min | **Yes, first-line** | — | | **Codeine** | IM/PO | 30–60 min | No | Weak opioid; prodrug requiring hepatic conversion; slower onset; not suitable for severe postop pain | | **Tramadol** | IV/IM/PO | 30–60 min | No | Weak opioid; monoamine reuptake inhibitor; risk of serotonin syndrome; not first-line for severe acute pain | | **Naloxone** | IV | Immediate | No — **antagonist** | Opioid antagonist, not agonist; used only for overdose reversal | **Clinical Pearl:** Standard postoperative morphine dosing: 2–4 mg IV every 2–4 hours PRN, or 5–10 mg IM every 3–4 hours. Titrate to pain relief; monitor respiratory rate and oxygen saturation. **Warning:** Codeine is a weak opioid and prodrug (converted to morphine by CYP2D6); it is inadequate for severe postoperative pain and has slower onset than morphine. Tramadol carries risk of serotonin syndrome and is not first-line for acute severe pain.