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.
- Use less reduction when switching solely because of uncontrolled pain without toxicity only after senior review; never use one automatic percentage for every case.
- Local formulary and specialist or pharmacy verification govern every conversion, especially transdermal fentanyl, oxycodone, hydromorphone, alfentanil, buprenorphine and methadone.
- For oral morphine, a traditional breakthrough starting point is about one-sixth of the regular 24-hour dose; local tables may use a range and renal disease changes the drug choice.
- Choose rescue route and onset for the episode. Pre-empt predictable incident pain and do not expect standard oral rescue to abort a flare peaking within minutes.
- Patch initiation and removal need overlap or washout instructions specific to the preparation and prior opioid; never improvise from a general ratio.
- The gold standard is a written calculation showing source table, dose reduction, rounding, rescue plan, last old dose, first new dose and monitoring, independently checked before prescribing.
Key red flags
Never convert from memory alone: ratios vary among guidelines, individuals, dose ranges and switching direction.
Methadone has non-linear conversion and a long variable half-life and must be initiated or rotated only by an experienced specialist.
A fentanyl or buprenorphine patch remains active after removal and heat or fever can increase absorption; document removal time and site.
Morphine and codeine metabolites accumulate in significant renal impairment, so an arithmetically correct dose may still be clinically unsafe.
Do not add rescue doses that were prescribed but not taken, and do not omit transdermal or infusion exposure from the previous 24-hour total.
Breakthrough doses given repeatedly before onset can stack, causing delayed respiratory depression without improving a very brief incident episode.
A decimal or microgram-to-milligram error with fentanyl or alfentanil can be fatal and requires an independent calculation check.
New somnolence, slowed breathing, pinpoint pupils, delirium or myoclonus after conversion is an urgent medication-safety event.
Investigation priorities
List actual scheduled, rescue, patch and infusion exposure with formulation, route, strength, timing and indication.
Management branches
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.
- Write old-stop and new-start times, rescue dose, monitoring and escalation thresholds, remove superseded prescriptions and review within the target drug's onset window.
Stable opioid need and route limitations make transdermal fentanyl or buprenorphine a considered option.
- Confirm opioid tolerance, stable requirement, skin and heat risks and calculate the patch strength through the product-specific local table with independent check.
- Document old opioid overlap or discontinuation and the rescue regimen, apply one labelled patch and record date, time, strength and site.
- Review analgesia and toxicity through onset, remove prior patches, reassess during fever or cachexia and follow product guidance when stopping or changing strength.