Respiratory depression or reduced GCS: stop the opioid, support the airway and breathing, and give titrated naloxone if needed (small doses in palliative care to avoid a crisis of pain). Review for accumulation, especially in renal impairment.
Conversions (approximate)
- Oral to IV or subcutaneous morphine: roughly divide the oral dose by 2
- Oral morphine to oral oxycodone: roughly divide by 1.5 to 2
- Always check a conversion chart and reduce for incomplete cross-tolerance
- Opioid-naive, acute pain: start low
Breakthrough dosing
- Breakthrough (PRN) dose is about one sixth of the total 24-hour background dose
- Reassess and titrate the background dose using 24-hour PRN use
- Renal impairment: avoid morphine if eGFR is low; consider oxycodone, or alfentanil or fentanyl with care
Standard prescribing
- Regular plus PRN, same opioid
- Prescribe a laxative and antiemetic
- Convert doses carefully
Caution
- Elderly or renal impairment: reduce or switch
- Oxycodone or alfentanil if poor renal function
- Review in the opioid-naive
Toxicity
- Drowsy, RR under 8, pinpoint pupils
- Naloxone (titrate in palliative care)
- Reassess dose and route
Safe steps
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1. Regular plus PRN
For ongoing severe pain, prescribe a regular (background) opioid and a breakthrough PRN of the correct size and route.
For ongoing severe pain, prescribe a regular (background) opioid and a breakthrough PRN of the correct size and route.
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2. Modified vs immediate release
Do not confuse MR (12-hourly) with immediate-release; do not crush MR preparations. Use IR for breakthrough and titration.
Do not confuse MR (12-hourly) with immediate-release; do not crush MR preparations. Use IR for breakthrough and titration.
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3. Anticipate side effects
Co-prescribe a laxative (constipation is universal) and an antiemetic as needed; warn about drowsiness and driving.
Co-prescribe a laxative (constipation is universal) and an antiemetic as needed; warn about drowsiness and driving.
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4. Review
Daily review of pain and side effects, a weaning plan for acute pain, and specialist palliative advice for complex cases.
Daily review of pain and side effects, a weaning plan for acute pain, and specialist palliative advice for complex cases.
Red flags for toxicity
- Drowsiness, confusion, myoclonus, pinpoint pupils
- Falling respiratory rate
- Worse in renal impairment and with other sedatives
Pitfalls
- Errors converting between opioids and routes
- Confusing MR with IR, or crushing MR tablets
- Morphine in significant renal impairment
- Forgetting a laxative
MedPrep - www.medprep.uk - Educational revision aid only. Not clinical guidance. Doses are adult examples; check the BNF, current guidelines and local policy, and seek senior advice. Nov 2026