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Opioid Toxicity & Safe Conversion
Toxicity triad: drowsiness + pinpoint pupils + RR <8. Renal failure accumulates morphine — switch to fentanyl/alfentanil/buprenorphine when eGFR <30. In patients on regular opioids, titrate naloxone in 20–40mcg increments to breathing, not…
Opioid Safety Pathway
The pathway
1 · Recognise toxicity
- Drowsy + miosis + RR <8
- Myoclonus, hallucinations = accumulation
- Check renal function + drug chart
2 · Graded response
- Rousable + RR ≥8 → omit doses, monitor sats/RR
- RR <8/unrousable → titrated naloxone
3 · Careful naloxone
- Dilute 400mcg to 10ml, give 0.5–1ml (20–40mcg) q2min
- Titrate to RR, not GCS
- Half-life shorter than opioid — may need repeats/infusion
4 · Fix the cause
- eGFR <30 → fentanyl/alfentanil/buprenorphine
- Moderate impairment → oxycodone cautiously
- Reduce converted dose 25–50% for cross-tolerance
5 · Convert accurately
- Oral morphine → SC morphine ÷2; → SC diamorphine ÷3
- Oral morphine → oral oxycodone ÷1.5–2
- Fentanyl 25mcg/hr ≈ 60–90mg oral morphine/24h
- Chart + second check, every time
6 · Monitor after changes
- Sedation score precedes respiratory depression
- RR + sats after dose changes
- Palliative care for complex cases
Drugs
| Drug | Dose | Route | Notes |
|---|---|---|---|
| Naloxone (titrated) | 20–40mcg increments q2min | IV | Dilute 400mcg→10ml. Full 400mcg only in arrest/apnoea. |
| Alfentanil | Specialist conversion | CSCI | Opioid of choice in severe renal failure (driver). |
| Oxycodone | Convert ÷1.5–2 from morphine | PO/SC | Moderate renal impairment; still caution eGFR <30. |
| Fentanyl patch | 25mcg/hr ≈ 60–90mg PO morphine | TOP | Slow on/off; heat ↑absorption; keep on in dying patients. |
When to escalate
RR <8 not responding to titrated naloxone — critical care,Toxicity in renal failure — switch opioid class + palliative advice,Complex conversions (methadone, high-dose, patches) — specialist input,Recurrent toxicity — root-cause the prescribing system
Reference: BNF opioid conversion guidance / Palliative Care Formulary (PCF)
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