Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Opioid conversion and breakthrough dosing
Palliative and end-of-life care · UK scope · Sources checked 27 Aug 2026 · Clinical 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.
Purpose and principles
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.
Opioid conversion is required when route fails, adverse effects limit treatment, organ function changes, adherence favours another formulation or pain remains difficult despite rational titration. It is also one of the highest-risk points in palliative prescribing. Equianalgesic tables summarise population estimates and use different rounding and ratios. Select the current local palliative formulary, document it and obtain pharmacy or specialist verification rather than combining figures from several sources.
Begin with the actual previous 24-hour exposure. List every regular and administered rescue dose by generic drug, formulation and route, including patches, infusions and patient-controlled boluses. Exclude unused prescribed doses. If the regimen or pain is rapidly changing, a single day may misrepresent stable requirement and senior review is needed. Convert components to one reference, commonly oral morphine equivalent, before calculating the target.
Indications, selection and cautions
Route-change conversion
Vomiting, dysphagia or malabsorption may require oral-to-subcutaneous conversion while the same analgesic need continues.
Toxicity-driven rotation
Hallucinations, myoclonus, hyperalgesia or sedation despite analgesia supports switching with an incomplete-cross-tolerance reduction and close observation.
Stable patch candidate
Consistent opioid requirement, unsuitable oral route and enough subcutaneous tissue may support transdermal treatment after specialist and formulary calculation.
Incident breakthrough
Brief predictable movement pain needs advance timing and possibly a rapid route rather than a larger slow maintenance dose.
Conversion discrepancy
Two table results, unexpected tablet burden, round-number jump or unit mismatch requires calculation to stop until independently resolved.
Post-switch toxicityRed flag
New somnolence, slowed breathing, pinpoint pupils, delirium or myoclonus after conversion is an urgent medication-safety event.
Red flags requiring action
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.
Assessment before treatment
01First-line 24-hour dose reconstructionFirst stepFirst line
Why
List actual scheduled, rescue, patch and infusion exposure with formulation, route, strength, timing and indication.
Interpretation and limitations
Use administered rather than merely prescribed doses and extend the review period when the prior day was clinically atypical.
02Current organ and toxicity assessment
Why
Review renal and hepatic function, hydration, frailty, sedation, cognition, myoclonus, breathing and interacting depressants.
Interpretation and limitations
These findings determine target drug, reduction and monitoring and can make a numerically valid conversion clinically inappropriate.
03Single-table equianalgesic calculation
Why
Convert previous exposure to the chosen reference and then to the target using one current local source.
Interpretation and limitations
Record table, ratio, direction and raw result; disagreement between sources requires pharmacy or specialist resolution, not averaging.
04Cross-tolerance and rounding review
Why
Choose a safety reduction based on toxicity, dose, frailty, organ function and reason for switch and round to measurable strengths.
Interpretation and limitations
Reduction is a clinical judgment rather than a fixed formula; document what risk the selected percentage addresses.
Treatment approach
01Opioid rotationReconcile, calculate, reduce and monitorFirst stepA switch of opioid or route is needed because of toxicity, route failure, organ function or inadequate response.+
1Reconstruct actual exposure, define the reason for switching and assess pain mechanism, toxicity, organ function, frailty and interacting medicines.
2Use one local conversion table, apply and document the clinically appropriate cross-tolerance reduction and obtain independent pharmacy or specialist verification.
3EscalationWrite old-stop and new-start times, rescue dose, monitoring and escalation thresholds, remove superseded prescriptions and review within the target drug's onset window.
02Breakthrough prescribingMatch dose and onset to the episodeTransient severe pain occurs despite an agreed maintenance regimen.+
1
Regimens, contraindications and interactions
Treats spontaneous breakthrough and provides information about whether background morphine remains adequate.
Immediate-release oral morphine breakthrough
A 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.
Avoid unchanged use in significant renal impairment, after a conversion or for dose stacking; frequent need, sedation or poor response requires review rather than automatic repetition.
Provides continuous analgesia when opioid requirement is stable and the oral route is unsuitable or burdensome.
Transdermal fentanyl for stable opioid need
Many 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.
Not for opioid-naive rapid titration; fever and external heat can increase absorption, cachexia and adhesion can alter delivery, and effect continues after patch removal.
Maintains opioid analgesia when swallowing or gastrointestinal absorption fails and morphine clearance remains suitable.
Subcutaneous morphine after route conversion
Complications, monitoring and follow-up
Observe pain, alertness, respiratory rate and effort, cognition and myoclonus at intervals matched to the old and new formulations' onset and offset.
Count and time breakthrough doses, recording response and whether episodes were spontaneous, incident or end-of-dose failure.
Check patch presence, strength, adhesion, date, time and site at every administration review and after bathing, fever or transfer.
Repeat renal and hepatic assessment after dehydration, infection or rapid decline and reconsider both maintenance and rescue drug choice.
Reconcile all charts and home supplies after the switch and cancel obsolete electronic and paper prescriptions to prevent parallel dosing.
Review constipation, nausea, falls, sleep and function as well as analgesia because equianalgesia does not imply equal adverse effects.
Document the calculation source, independent checker and clinical reduction so the next prescriber can safely understand the regimen.
Special situations
Equianalgesic is approximate
Tables estimate population potency and cannot predict one person's absorption, tolerance, genetics, organ clearance and pain mechanism.
Direction can change ratio
Some source tables use different ratios for switching to and from the same opioid, so reverse arithmetic may be unsafe.
Cross-tolerance is incomplete
Reducing the calculated new opioid creates safety space because tolerance to adverse effects does not transfer predictably.
Patches have pharmacological tails
A removed patch leaves drug in skin and systemic circulation, so immediate full replacement dosing can overlap dangerously.
Rescue is not a fraction alone
Drug, route, onset, minimum interval, episode mechanism and organ function complete a safe breakthrough prescription.
Written workings prevent recurrence
Showing source values, units and decisions allows checking at discharge and exposes when a later prescriber used a different table.
Common pitfalls
01
Converting from memory or averaging two conflicting tables.
02
Adding prescribed but unused rescue doses to actual exposure.
03
Forgetting a patch or infusion when calculating the previous total.
04
Using the raw equianalgesic result without considering cross-tolerance and toxicity.
05
Reversing a one-direction conversion ratio automatically.
06
Treating 25 micrograms as 25 milligrams in a high-potency opioid calculation.
07
Starting a patch for rapidly changing pain or in an opioid-naive patient.
08
Leaving the old rescue opioid active after a maintenance switch without review.
09
Increasing background dose for short predictable incident pain.
10
Attempting a methadone conversion without specialist responsibility.
Practice
Two practice questions
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Question 1 of 2
0 correct
Palliative and end-of-life careOriginal SBA
Safe opioid rotation method
A frail patient with morphine neurotoxicity and worsening sedation needs rotation to another strong opioid. Which conversion approach is safest?
Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources
Sources and review status
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.
Illustrative arithmetic can explain the process but must not substitute for a patient-specific check. Many UK palliative tables approximate 60 mg oral morphine in 24 hours to 30 mg subcutaneous morphine in 24 hours, or to a fentanyl patch around 25 micrograms/hour. Oral oxycodone is often estimated as roughly 1.5 to 2 times as potent as oral morphine. Exact ratios and rounding vary, especially at high doses and by direction of switching.
The equianalgesic result is not automatically the prescribed target. Incomplete cross-tolerance means tolerance to one opioid does not transfer fully to another. Frailty, toxicity, high total exposure and renal or hepatic impairment support a reduction often in the region of 25 to 50 percent, followed by rescue and close titration. The appropriate reduction depends on why the switch is happening and should be agreed with an experienced prescriber.
Breakthrough calculation begins only after the maintenance plan is defined. A commonly used oral morphine rescue is one-sixth of the total regular 24-hour oral morphine dose, rounded to an available safe preparation. Other opioids and patches use their own local rescue tables. Frequency, minimum interval and escalation action must be explicit. Frequent use may reflect under-treated background pain, but incident pain, wrong mechanism and disease emergency must be excluded first.
Transdermal therapy needs temporal planning. Fentanyl patches are for stable opioid requirements, not rapid titration or opioid-naive acute pain. Absorption rises slowly after application and persists after removal. Fever, external heat, adhesion, cachexia and skin condition can change exposure. Follow the product-specific overlap and removal schedule, record date, time, strength and site and ensure old patches are removed and folded safely for disposal.
Methadone is an exception that illustrates why ratios cannot be memorised. Potency relative to morphine increases non-linearly at higher exposure, half-life is prolonged and variable, and QT and interaction risks are substantial. Rotation should be undertaken by a specialist service with an explicit schedule and monitoring. Alfentanil and other high-potency microgram-dose opioids similarly demand independent checks and renal-aware specialist prescribing.
Key points
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.
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.
05Breakthrough and transition plan
Why
Calculate rescue in the target opioid, define interval and maximum action and specify last old and first new dose or patch overlap.
Interpretation and limitations
Maintenance, rescue and transition must be coherent; a correct maintenance conversion can still fail through unsafe overlap or obsolete rescue.
06Independent clinical check
Why
Have an authorised second practitioner or pharmacist verify source values, arithmetic, units, formulation, prescription and administration plan.
Interpretation and limitations
This documented check is the gold-standard safety barrier for high-risk or unfamiliar conversions and all microgram-potency regimens.
Classify spontaneous, incident or end-dose failure and record onset, duration, predictability, frequency and response to prior rescue.
2Calculate rescue from the current local opioid table, choose a route whose onset fits and schedule pre-emptively for predictable triggers when safe.
3Set interval and maximum-action instructions, monitor sedation and review repeated need for background adjustment or cause-directed treatment.
03Patch switchControl delayed onset and offsetStable opioid need and route limitations make transdermal fentanyl or buprenorphine a considered option.+
1Confirm opioid tolerance, stable requirement, skin and heat risks and calculate the patch strength through the product-specific local table with independent check.
2Document old opioid overlap or discontinuation and the rescue regimen, apply one labelled patch and record date, time, strength and site.
3Review analgesia and toxicity through onset, remove prior patches, reassess during fever or cachexia and follow product guidance when stopping or changing strength.
04Suspected errorStop administration and reconstruct exposureClinical response is unexpected or a unit, ratio, formulation, patch or chart discrepancy is found.+
1Withhold further doses, assess airway, breathing, consciousness and pain and summon urgent help when toxicity or withdrawal is clinically significant.
2Collect charts, pumps, patches, bottles and administration records and calculate the chronological exposure with pharmacy and a senior clinician.
3Treat toxicity, correct the regimen, communicate openly under the local incident process and increase monitoring until both old and new opioid effects are accounted for.
Many palliative formularies approximate total subcutaneous morphine over 24 hours as half the total oral morphine over 24 hours, but calculate using the current local route-conversion table and reduce or change opioid when renal impairment or toxicity makes morphine unsafe.
Include all rescue doses, specify total over 24 hours rather than an hourly ambiguity and prescribe separate subcutaneous rescue coherently; obtain an independent check.
May help selected complex nociceptive or neuropathic pain and opioid toxicity when specialist expertise is available.
Methadone only under specialist conversion
There is no safe fixed morphine-to-methadone ratio for generalist use; the initiating specialist must provide the patient-specific staged regimen, rescue plan and ECG or interaction monitoring in writing.
Non-linear potency, variable long half-life, accumulation, QT prolongation and CYP interactions make unsupervised starting, titration or conversion dangerous.