Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 27 Aug 2026Clinical review pending
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Conversion error or dose stacking
Unexpected sedation, respiratory depression, confusion, myoclonus or duplicated opioid after a switch may indicate a decimal, route, formulation, patch or cross-tolerance error.
Action: Stop further opioid, call urgent clinical or resuscitation help and support airway and breathing. Reconstruct every dose, route, patch and administration time; use titrated naloxone when significant respiratory depression requires it, and involve pharmacy or specialist palliative care before restarting a corrected regimen.
Synopsis
Convert opioid regimens through a transparent, independently checked process, account for route, formulation, incomplete cross-tolerance and organ function, and prescribe breakthrough treatment whose dose and onset match the pain episode without false precision.
Conversion estimates equianalgesic exposure; they are starting hypotheses, not exact biological equivalence for an individual patient.
First-line process: identify indication, reconcile actual previous 24-hour doses, convert to an oral-morphine equivalent using one current local table, then calculate the target drug and route.
Reduce the calculated target when incomplete cross-tolerance, frailty, high dose, toxicity or organ impairment increases risk, commonly by about 25 to 50 percent under specialist guidance.
Key red flags
Never convert from memory alone: ratios vary among guidelines, individuals, dose ranges and switching direction.
Post-switch toxicity
New somnolence, slowed breathing, pinpoint pupils, delirium or myoclonus after conversion is an urgent medication-safety event.
Investigation priorities
01
First-line 24-hour dose reconstructionFirst stepFirst line
List actual scheduled, rescue, patch and infusion exposure with formulation, route, strength, timing and indication.
Management branches
Opioid rotationReconcile, calculate, reduce and monitor
A switch of opioid or route is needed because of toxicity, route failure, organ function or inadequate response.
Reconstruct actual exposure, define the reason for switching and assess pain mechanism, toxicity, organ function, frailty and interacting medicines.
Use one local conversion table, apply and document the clinically appropriate cross-tolerance reduction and obtain independent pharmacy or specialist verification.
Patch switchControl delayed onset and offset
Stable opioid need and route limitations make transdermal fentanyl or buprenorphine a considered option.
Key medicines
Immediate-release oral morphine breakthroughA common palliative starting calculation is about one-sixth of the regular 24-hour oral morphine dose for each breakthrough, rounded to a measurable safe preparation and verified against the current local formulary; the interval and escalation limit must be prescribed explicitly.
Transdermal fentanyl for stable opioid needMany UK conversion tables approximate 60 mg oral morphine per 24 hours to fentanyl 25 micrograms/hour, but the selected patch, overlap and rescue must follow the current local table, product information and independent pharmacy or specialist check.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.