A 58-year-old man with moderate-to-severe cancer pain inadequately controlled on non-opioid analgesics is started on opioid therapy. He has no history of opioid use. Which opioid is the drug of choice for initiating opioid analgesia in this patient?

Explanation

## Opioid Selection in Opioid-Naïve Cancer Patients **Key Point:** Morphine is the gold-standard first-line opioid for initiating opioid therapy in opioid-naïve patients with moderate-to-severe cancer pain. ### Why Morphine? 1. **Predictable pharmacokinetics** — oral and parenteral formulations with well-characterized absorption and metabolism 2. **Flexible dosing** — immediate-release (IR) for titration, extended-release (ER) for maintenance 3. **No active metabolites of concern** — morphine-3-glucuronide and morphine-6-glucuronide are renally cleared; M6G has analgesic activity but is manageable 4. **Extensive clinical experience** — decades of use in cancer pain; safety profile well-established 5. **Reversible** — can be titrated up or down; no depot formulation in initial therapy 6. **Cost-effective** — widely available, affordable ### Comparison with Alternatives | Feature | Morphine | Fentanyl Patch | Methadone | Buprenorphine | |---------|----------|---|----------|---------------| | **First-line in opioid-naïve?** | Yes | No | No | No | | **Titration flexibility** | Excellent (IR available) | Poor (fixed-dose patch) | Difficult (long t½, accumulation) | Limited (partial agonist ceiling) | | **Onset** | 30–60 min (PO) | 12–24 hrs (patch) | 4–6 hrs (slow accumulation) | 30–60 min (SL) | | **Use case** | Initiation, moderate–severe pain | Stable, chronic pain | Opioid addiction, refractory pain | Mild–moderate pain, addiction | **High-Yield:** WHO analgesic ladder recommends morphine as the strong opioid of choice for cancer pain management. **Clinical Pearl:** Start with immediate-release morphine 5–10 mg PO every 4–6 hours, titrate by 25–50% every 24–48 hours until pain controlled, then convert to extended-release formulation at equianalgesic dose. **Warning:** Fentanyl patches are contraindicated in opioid-naïve patients due to risk of fatal overdose from unpredictable absorption; they are reserved for opioid-tolerant patients with stable pain.