Methadone Conversion Dose Bands Interpreter

Methadone’s conversion factor is not a constant: it rises with the dose. This page prints the four dose-banded factors from CDC’s own conversion file against the single factor its 2022 guideline replaced them with, and refuses the direction that is specialist practice.

Four factors for one drug, and why

Methadone to morphine milligram equivalents: CDC’s own two answers

Morphine to methadone: the published bands, printed and not applied

A factor that is not a constant

Every other opioid in this category has a potency factor that sources argue about. Methadone does not have one at all. Its potency relative to morphine rises with the dose being converted, so the only honest representation is a set of bands, and the bands disagree between documents and even between two documents from the same organisation.

CDC’s pre-2022 conversion file made the factor depend on the methadone dose: 4 from 1 to 20 mg a day, 8 from 21 to 40, 10 from 41 to 60, and 12 at 61 mg a day and above. That produces a figure that rises faster than the dose, because the factor steps up underneath it — doubling a methadone dose from 20 to 40 mg a day multiplies the computed equivalent by four. The 2022 guideline replaced all four bands with a single factor of 4.7, and MO HealthNet’s 2023 notice of the change records the old value as 3, a third CDC-derived number. At 80 mg of methadone a day, the banded answer and the flat answer differ by a factor of 2.55 for the same patient on the same day.

The other direction — putting a patient’s morphine onto methadone — is where the real danger lives, and this page refuses it. The two sources read for it describe different curves: Wellington ICU’s Appendix 6 bands it 4 to 1 below 90 mg of oral morphine a day, 8 to 1 from 91 to 300 and 12 to 1 from 301 to 600, while MSD’s equianalgesic table describes a ratio rising from about 2 to 1 below 30 mg of oral morphine equivalent a day to about 20 to 1 at 1000 mg and above. MSD then applies a reduction of 75 to 90 per cent on top of whichever ratio is used, against 50 per cent for other switches, and Fine and Portenoy’s scheme excepts methadone from the standard first reduction altogether. The Faculty of Pain Medicine simply writes “varies” where every other drug has a number, and the Scottish Palliative Care Guidelines say methadone conversions are complicated and should always be made with specialist advice.

Two properties of the drug sit behind all of that. Its half-life is long and variable, so concentrations continue to rise for days after a change and a conversion that looks correct on the first day may not be on the fourth — the hazard is delayed, which is exactly the kind of hazard a one-line ratio hides. And it prolongs the QT interval, a risk entirely unrelated to the opioid arithmetic and monitored separately with a rate-corrected QT and its alternative corrections. Every published conversion factor on this page is a population approximation with wide interindividual variability. The factor that fits the average of a cohort can be out by twofold or more in one person, because opioid absorption, clearance, active-metabolite handling and receptor pharmacology all differ between individuals. The equianalgesic tables these factors descend from were largely derived from single-dose studies in opioid-naive or acute-pain patients, and they are applied in practice to chronic, repeated dosing in people who are already tolerant — a use the original studies were never designed to support. Published practice when changing from one opioid to another is to reduce the calculated equivalent, and the reduction is applied after the equivalence rather than instead of it. The reason is incomplete cross-tolerance: tolerance to one opioid does not transfer fully to another, so the arithmetic equivalent over-estimates what the patient already tolerates. The Faculty of Pain Medicine puts the cut at 25 to 50 per cent, and at least 50 per cent above about 500 mg of oral morphine equivalent a day or in the frail and elderly; the other five sources read for this page put the first cut between 25 and 50 per cent and none puts it at zero; and MSD’s table raises it to 75 to 90 per cent for methadone. The figure this page returns is an arithmetic equivalence and nothing else. It is not a dose, not a target and not a limit, and no part of this page says what any patient’s dose ought to be. Your own formulary, local conversion chart or specialist pain or palliative care service governs: where it differs from anything here, it wins. The flat 4.7 that replaced the bands is used by the MME page, which shows both CDC answers side by side.

Frequently asked questions

Related calculators

References

1. CDC. 2022 CDC Clinical Practice Guideline for Prescribing Opioids Implementation Guide, ConversionFactors library. The pre-2022 factor set, read out of the library’s own CQL: codeine 0.15, hydrocodone 1, hydromorphone 4, morphine 1, oxycodone 1.5, oxymorphone 3, transdermal fentanyl 2.4 per microgram an hour, and methadone banded on the daily methadone dose — 4 from 1 to 20 mg a day, 8 from 21 to 40, 10 from 41 to 60, 12 at 61 and above. A dose below 1 mg a day returns a message rather than a factor.
2. Maryland Department of Health, Prescription Drug Monitoring Program. MME Fact Sheet. Reproduces the pre-2022 CDC factor set row for row, adds buccal, sublingual and lozenge fentanyl at 0.13 per microgram, lists no factor for tramadol, and states of buprenorphine that “There is not a calculation to identify equivalency therefore MME is not available for buprenorphine products”. Used here as the independent corroboration of CDC’s own CQL library, which renders truncated. At 50 MME a day it advises monitoring pain and function more frequently and discussing dose reduction, tapering or discontinuation if benefits do not outweigh harms.
3. 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”.
4. MO HealthNet Division, Missouri Department of Social Services. Morphine Milligram Equivalent (MME) Factor Update for Hydromorphone, Methadone, and Tramadol, effective 17 September 2023, citing the CDC 2022 guideline. Records the three changes individually: hydromorphone 4 to 5, methadone 3 to 4.7, tramadol 0.1 to 0.2. The only document read for this batch that states the old and the new values side by side, which is what makes CDC’s disagreement with itself checkable rather than inferred.
5. 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.
6. Wellington ICU Drug Manual, Appendix 6: opioid equivalence. Publishes the 24-hour oral morphine to oral methadone ratio in three bands — 4:1 below 90 mg of morphine, 8:1 from 91 to 300 mg, 12:1 from 301 to 600 mg — with oral to intramuscular or intravenous methadone at 2:1, and the instruction to calculate the equianalgesic dose and then cut it by 25 to 50 per cent. Its fentanyl rows match 25 micrograms an hour to 50 mg of oral or 16 mg of intravenous morphine over 24 hours. The appendix’s main table is published as an image rather than as text and was therefore not readable; only the figures quoted here were read as text.
7. 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”.

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/