A 58-year-old man with metastatic pancreatic cancer presents to the palliative care clinic with severe pain (8/10). He has been on paracetamol 1 g QID and ibuprofen 400 mg TDS for 2 weeks with inadequate relief. On examination, he is cachectic, BP 110/70 mmHg, HR 88/min, RR 16/min. Liver function tests show mild elevation of transaminases. You decide to initiate opioid therapy. Which of the following is the most appropriate first-line opioid and route for this patient?

Explanation

## Opioid Selection in Cancer Pain Management **Key Point:** In opioid-naive patients with cancer pain, immediate-release oral morphine is the WHO gold standard first-line agent. It allows rapid dose titration, flexible dosing, and assessment of individual opioid sensitivity before committing to long-acting formulations. ### Rationale for Correct Answer Morphine 10 mg oral immediate-release 4-hourly with 5 mg rescue doses is appropriate because: 1. **Opioid-naive patient**: Requires starting at low-to-moderate doses to establish tolerance and assess side effects 2. **Oral route preferred**: Non-invasive, maintains dignity, allows self-administration 3. **Immediate-release formulation**: Permits rapid titration (increase by 25–50% every 24–48 hours based on pain and tolerability) 4. **Rescue dosing**: 10–20% of 4-hourly dose as breakthrough medication (here, 5 mg) is standard 5. **Liver function**: Mild transaminitis does not contraindicate morphine; morphine is metabolized hepatically but tolerated in mild liver disease **High-Yield:** The WHO analgesic ladder recommends: non-opioid → weak opioid (codeine) → strong opioid (morphine). This patient has failed step 1; morphine is step 3. ### Why Other Routes/Agents Are Suboptimal | Option | Why Not First-Line | |--------|-------------------| | **IV morphine bolus + infusion** | Reserved for acute severe pain, terminal sedation, or when oral route unavailable. Not standard initiation in ambulatory palliative care. | | **Fentanyl transdermal patch** | Contraindicated in opioid-naive patients; risk of overdose due to high potency (50–100× morphine). Used only after stable morphine dose established. | | **Methadone once daily** | Long half-life (15–60 hours), high risk of accumulation and overdose in non-tolerant patients. Requires specialist dosing; not first-line. | **Clinical Pearl:** Transdermal fentanyl is appropriate *after* the patient is stabilized on oral morphine equivalent dose (e.g., ≥60 mg/day) and pain is well-controlled. Switching to fentanyl patch at this stage would be premature and dangerous. ### Titration Strategy ```mermaid flowchart TD A[Opioid-naive patient with severe pain]:::outcome --> B[Start morphine 10 mg PO 4-hourly + 5 mg rescue]:::action B --> C{Pain controlled at 24-48 hrs?}:::decision C -->|No| D[Increase total daily dose by 25-50%]:::action C -->|Yes| E[Continue current dose]:::action D --> F{Stable dose reached?}:::decision F -->|Yes| G[Switch to long-acting formulation<br/>e.g., morphine ER 12-hourly]:::action F -->|No| D G --> H[Maintain rescue doses]:::action ``` **Mnemonic: MORPHINE START** — **M**onitored titration, **O**ral route, **R**escue doses, **P**ain reassessment, **H**igh-yield first-line, **I**mmediate-release, **N**o long-acting initially, **E**scalate by 25–50%. **Tip:** Always prescribe breakthrough doses (10–20% of 4-hourly dose) and educate the patient that it is *not* a sign of addiction to use rescue doses; they reflect inadequate baseline analgesia and guide titration.