Fentanyl Patch to Oral Morphine Conversion Calculator
Fentanyl Patch to Oral Morphine Conversion Calculator
A fentanyl patch rate expressed as oral morphine a day by the published single factor and by both of the manufacturer’s bands — which are 2.49-fold apart, and which the Summary of Product Characteristics says must only be read in the other direction.
Patch rate as oral morphine a day, three published tables
13 strengths, 3 tablesA 50 micrograms an hour fentanyl patch, read as oral morphine a day
One factor everyone agrees on, two bands 2.49-fold apart
Faculty of Pain Medicine and BNF table: 12, 25, 50, 75 and 100 micrograms an hour against 30, 60, 120, 180 and 240 mg a day — which is 2.4 throughout
CDC 2022 and CDC pre-2022: transdermal fentanyl 2.4 per microgram an hour
Manufacturer, stable patient (about 100 to 1): 45–89, 90–149, 150–209 and 210–269 mg a day map to 25, 50, 75 and 100 micrograms an hour; 44 mg or less maps to 12
Manufacturer, rotation or less stable (about 150 to 1): 90–134, 135–224, 225–314 and 315–404 mg a day map to the same four strengths; below 90 maps to 12
- 2.4, and why it is 100 to 1
- 50 micrograms an hour is 1.2 mg of fentanyl over 24 hours, and the table pairs it with about 120 mg of oral morphine — a ratio of 100 to 1. The factor of 2.4 is that same statement per microgram an hour, and the Faculty of Pain Medicine, the BNF-derived charts and both CDC factor sets all carry it
- why the manufacturer’s table is wider
- it is deliberately conservative and it is a step table rather than a factor, so each patch strength covers a range of previous morphine doses. The rotation table is built at about 150 to 1 rather than 100 to 1, which is a 1.5-fold safety margin on exactly the patients in whom a conversion is most likely to go wrong
- one-directional, and why
- the Summary of Product Characteristics states that its tables “should only be used to convert from other opioids to Fencino and not from Fencino to other therapies to avoid overestimating the new analgesic dose and potentially causing overdose”. Read forwards they are cautious; read backwards the same caution becomes an over-estimate of the morphine the patch is worth
- heat
- “Fentanyl concentrations may increase if the skin temperature increases”, with “a potential for temperature-dependent increases in fentanyl released from the system resulting in possible overdose and death”. Fever, a heat pad, an electric blanket, a heated water bed, a hot bath and a sauna all count. No conversion factor has a term for this
- the depot, and the 20 to 27 hours after removal
- the drug reaching the circulation comes from a reservoir in the skin as well as from the patch, so removing the patch does not stop the exposure. “It may take 20 hours or more for the fentanyl serum concentrations to decrease 50%”, and the apparent half-life after a 72-hour application is 20 to 27 hours — two to three times the intravenous figure
- a used patch is not an empty patch
- the Summary of Product Characteristics describes the patch as containing “an active substance in an amount that can be fatal, especially to a child”, and directs that a removed patch be folded adhesive-side onto itself before disposal. A patch worn for its full period still holds drug
- not for an opioid-naive patient
- the BNSSG chart states that its table is not for opioid-naive patients or for those stable on immediate-release morphine for only a few weeks, and that transdermal fentanyl is not used in opioid-naive patients with non-cancer pain. A conversion figure says nothing about whether the patient should be on a patch at all
Worked example
A 50 micrograms an hour fentanyl patch, read as oral morphine a day
Faculty of Pain Medicine, BNF and both CDC factor sets, 2.4 per microgram an hour: 50 × 2.4 = 120.0 mg of oral morphine a day
Manufacturer's stable-patient table maps 90 to 149 mg a day onto this strength, so read backwards it is 90 to 149 mg
Manufacturer's rotation table maps 135 to 224 mg a day onto it, so read backwards it is 135 to 224 mg
Highest ÷ lowest = 224 ÷ 90 = 2.49-fold across the published tables for one patch strength. Every one of those numbers is correctly read off a published table
The 12 micrograms an hour patch: 12.5 × 2.4 = 30.0 mg, which is exactly what the Faculty of Pain Medicine table prints. Using the labelled 12 rather than the nominal 12.5 returns 28.8 — a 4 per cent error on the commonest strength
A 100 micrograms an hour patch: 240.0 mg by the factor, 210 to 269 by the stable table and 315 to 404 by the rotation table. The spread is 1.92-fold here and 2.49-fold at 50 micrograms an hour, so it is not constant across the range
Two patches, a 25 and a 50, are 75 micrograms an hour and 75 × 2.4 = 180.0 mg — the rates add; the equivalents are not read off separately and summed from the band table, which would produce two overlapping ranges
In the other direction the page returns nothing at all, because the manufacturer's table says so
Every published fentanyl patch equivalence, by source
| Patch, micrograms an hour | Faculty of Pain Medicine, BNF and CDC, at 2.4 | Manufacturer, stable patient (mg a day) | Manufacturer, rotation or less stable (mg a day) | Highest ÷ lowest |
|---|---|---|---|---|
| 12 (nominally 12.5) | 30.0 | 44 or less | below 90 | not computable |
| 25 | 60.0 | 45 to 89 | 90 to 134 | 2.98 |
| 50 | 120.0 | 90 to 149 | 135 to 224 | 2.49 |
| 75 | 180.0 | 150 to 209 | 225 to 314 | 2.09 |
| 100 | 240.0 | 210 to 269 | 315 to 404 | 1.92 |
| 125 | 300.0 | 270 to 329 | 405 to 494 | 1.83 |
| 150 | 360.0 | 330 to 389 | 495 to 584 | 1.77 |
| 175 | 420.0 | 390 to 449 | 585 to 674 | 1.73 |
| 200 | 480.0 | 450 to 509 | 675 to 764 | 1.70 |
| 225 | 540.0 | 510 to 569 | 765 to 854 | 1.67 |
| 250 | 600.0 | 570 to 629 | 855 to 944 | 1.66 |
| 275 | 660.0 | 630 to 689 | 945 to 1034 | 1.64 |
| 300 | 720.0 | 690 to 749 | 1035 to 1124 | 1.63 |
The hazards a conversion factor has no term for
| Hazard | What the Summary of Product Characteristics says |
|---|---|
| External heat and fever | “Fentanyl concentrations may increase if the skin temperature increases”, with “a potential for temperature-dependent increases in fentanyl released from the system resulting in possible overdose and death”. Heating pads, electric blankets and heated water beds are named |
| The skin depot after removal | “It may take 20 hours or more for the fentanyl serum concentrations to decrease 50%”. The apparent half-life after a 72-hour application is 20 to 27 hours, about two to three times the intravenous value, because absorption continues from the depot |
| A used patch | The patch “contains an active substance in an amount that can be fatal, especially to a child”; removed patches are folded adhesive-side onto themselves before disposal |
| Naloxone’s duration against the patch’s | Not from the Summary of Product Characteristics but the arithmetic consequence of the row above: a depot that keeps releasing for 20 hours or more outlasts a single dose of a short-acting antagonist, which is the same point the toxidrome page makes about long-acting opioids |
| Opioid-naive patients | The BNSSG chart states the conversion table is not for opioid-naive patients or those stable on immediate-release morphine for only a few weeks, and that transdermal fentanyl is not used in opioid-naive patients with non-cancer pain |
A range, a direction, and a reservoir in the skin
Transdermal fentanyl is the opioid most often converted and the one least suited to a conversion factor. The single factor in routine use is 2.4 mg of oral morphine a day for every microgram an hour of patch, equivalent to a potency ratio of about 100 to 1, and it is the one figure in this whole category that every source read agrees on: the Faculty of Pain Medicine’s table, the BNF-derived charts, CDC’s 2022 table and CDC’s pre-2022 conversion file all carry 2.4. A 25 micrograms an hour patch is about 60 mg of oral morphine a day, a 50 about 120, a 100 about 240.
The manufacturer does not publish a factor. It publishes two step tables, each mapping a range of previous 24-hour oral morphine doses onto a patch strength, and the two are built at different ratios: about 100 to 1 for a patient on stable, well tolerated opioid therapy and about 150 to 1 for opioid rotation or a less clinically stable patient. Read backwards, the 50 micrograms an hour patch is worth 90 to 149 mg of morphine by one table and 135 to 224 by the other, a 2.49-fold spread on one strength. That conservatism is the point of the tables and it is why the Summary of Product Characteristics says they may only be read in one direction, in those words: “Tables 1, 2, and 3 should only be used to convert from other opioids to Fencino and not from Fencino to other therapies to avoid overestimating the new analgesic dose and potentially causing overdose.” This page therefore refuses the second direction outright and shows the bands inverted only so the width of the published uncertainty is visible.
Three practical hazards belong on this page because no factor can carry them. Absorption is temperature-dependent: the Summary of Product Characteristics warns of “a potential for temperature-dependent increases in fentanyl released from the system resulting in possible overdose and death”, so fever, a heat pad or a hot bath changes the delivered dose without changing the patch. The patch creates a reservoir in the skin, so removing it does not stop the exposure — “It may take 20 hours or more for the fentanyl serum concentrations to decrease 50%”, and the apparent half-life after removal is 20 to 27 hours, two to three times the intravenous value. And a used patch still contains “an active substance in an amount that can be fatal, especially to a child”.
These are population approximations; the published cross-tolerance reduction applies after any equivalence; your own formulary governs. The notes below set all three out in full. The oral factors that feed into any patch conversion are on the oral morphine equivalent page, and the long-acting-opioid problem the depot creates is the same one described on the toxidrome identifier.
Frequently asked questions
How much oral morphine is a fentanyl patch worth?
By the single factor every source read for this page agrees on, 2.4 mg of oral morphine a day per microgram an hour: 30 mg for the 12 patch, 60 for the 25, 120 for the 50, 180 for the 75 and 240 for the 100. The manufacturer publishes bands rather than a factor, and read backwards those bands make the 50 patch worth anywhere from 90 to 224 mg a day. The honest answer is a range, and the range is about 2.5-fold wide.
Why does this page refuse to convert the other way?
Because the document that answers that question says it must not be done indirectly. The Summary of Product Characteristics states that its tables “should only be used to convert from other opioids to Fencino and not from Fencino to other therapies to avoid overestimating the new analgesic dose and potentially causing overdose”. The tables are deliberately conservative in their own direction, and a conservative table read backwards systematically over-states the morphine a patch is worth.
Why is the 12 microgram patch entered as 12.5?
Because that is the rate it nominally delivers, and because the published tables were built on it: 12.5 × 2.4 is exactly the 30 mg a day that the Faculty of Pain Medicine and BNF table prints against that strength. Entering the labelled 12 returns 28.8, a 4 per cent error on the strength most often used first.
Does a patch stop working when it is removed?
No, and this is the practical trap on this drug. Fentanyl continues to be absorbed from a reservoir in the skin after the patch is off: the Summary of Product Characteristics says “It may take 20 hours or more for the fentanyl serum concentrations to decrease 50%”, and reports an apparent half-life after a 72-hour application of 20 to 27 hours, two to three times the intravenous figure. Anything whose duration is shorter than that — including a single dose of a short-acting antagonist — will be outlasted by the depot.
Does heat really change the dose?
The Summary of Product Characteristics treats it as a serious hazard: “Fentanyl concentrations may increase if the skin temperature increases”, with “a potential for temperature-dependent increases in fentanyl released from the system resulting in possible overdose and death”, and it names heating pads, electric blankets and heated water beds. Fever does the same thing. No conversion factor has a term for body temperature, which is one more reason the equivalence is a range rather than a number.
Related calculators
References
- Fencino 100 micrograms/hour Transdermal Patch. Summary of Product Characteristics, electronic Medicines Compendium. Table 3, for a patient on stable, well tolerated opioid therapy, matches 44 mg of oral morphine a day or less to a 12 microgram an hour patch, then 45–89, 90–149, 150–209 and 210–269 mg to 25, 50, 75 and 100; Table 2, for rotation or a less stable patient, matches below 90, then 90–134, 135–224, 225–314 and 315–404 mg to the same strengths. The warning that makes this calculator one-directional: “Tables 1, 2, and 3 should only be used to convert from other opioids to Fencino and not from Fencino to other therapies to avoid overestimating the new analgesic dose and potentially causing overdose.” Also: “Fentanyl concentrations may increase if the skin temperature increases”, with “a potential for temperature-dependent increases in fentanyl released from the system resulting in possible overdose and death”; after removal “It may take 20 hours or more for the fentanyl serum concentrations to decrease 50%”, a post-application half-life of 20 to 27 hours, two to three times the intravenous value; and the patch “contains an active substance in an amount that can be fatal, especially to a child”.
- Faculty of Pain Medicine of the Royal College of Anaesthetists. Opioids Aware: dose equivalents and changing opioids. Oral potencies, reviewed March 2023 against the BNF: codeine 0.1, dihydrocodeine 0.1, hydromorphone 5, morphine 1, oxycodone 1.5, tapentadol 0.4, tramadol 0.1, methadone “varies” with specialist advice required. Transdermal fentanyl 12, 25, 50, 75 and 100 micrograms an hour against 30, 60, 120, 180 and 240 mg of oral morphine a day. Conversion factors are an approximate guide only “because data are incomplete and individual variation is significant”; in most switches the calculated equivalent is cut by 25 to 50 per cent, and by at least 50 per cent above about 500 mg of oral morphine equivalent a day or in the elderly or frail; and “Opioid rotation is not recommended if a patient has responded to one opioid”.
- NHS Bristol, North Somerset and South Gloucestershire ICB. Opioid conversion charts — adults, 2024, version 3.1. Prints the fentanyl and buprenorphine patch equivalences in four columns at once — BNF/Faculty of Pain Medicine, the Summary of Product Characteristics band for a stable patient, the band for rotation or a less stable patient, and a local figure — so the disagreement is visible on one page. Potencies: codeine 0.1, dihydrocodeine 0.1, tramadol 0.1, oral oxycodone 1.5, tapentadol 0.4, hydromorphone 5. States that the calculated equivalent dose is reduced in most cases when switching, and that its table is not for opioid-naive patients.
- Dowell D, Ragan KR, Jones CM, Baldwin GT, Chou R. CDC Clinical Practice Guideline for Prescribing Opioids for Pain — United States, 2022. MMWR Recomm Rep. 2022;71(RR-3). Its conversion table, reproduced in CDC’s own 2022 Implementation Guide, reads: codeine 0.15, transdermal fentanyl 2.4 per microgram an hour, hydrocodone 1, hydromorphone 5, methadone 4.7, morphine 1, oxycodone 1.5, oxymorphone 3, tapentadol 0.4, tramadol 0.2. Of its seven cautions, the second is “Equianalgesic dose conversions are only estimates”, the third “Do not use the calculated dose in MMEs to determine the doses to use when converting one opioid to another”, and the seventh “These conversion factors should not be applied to dosage decisions related to the management of opioid use disorder”.
- MSD Manuals Professional Version. Equianalgesic Doses of Opioid Analgesics. Parenteral against oral: morphine 10 to 30 mg, codeine 130 to 200, hydromorphone 1.5 to 7.5, methadone 10 to 20, oxycodone 15 to 20, oxymorphone 1 to 15. Its footnotes state that the equivalences come from single-dose studies and clinical experience and are approximations; that on changing opioid the equianalgesic dose is cut by 50 per cent, and by 75 to 90 per cent for methadone; and that the morphine-to-methadone ratio is non-linear, rising from about 2:1 below 30 mg of oral morphine equivalent a day to about 20:1 at 1000 mg a day and above. Its oral oxymorphone figure of 15 mg against 30 mg of morphine implies a potency of 2, where CDC publishes 3.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/