Dose equivalents and changing opioids
- OME (Oral Morphine Equivalent) is a commonly used reference frame for considering dosing.
- An OME > 50mg requires close consideration.
- An individualised approach is necessary.
- Switching from one opioid to another should be supervised by a healthcare practitioner with adequate competence and sufficient experience.
- Opioid rotation or switching may be considered if a patient obtains pain relief with one opioid and is suffering severe adverse effects.
- When converting from one opioid to another, the initial dose depends on the relative potency of the two drugs and the route of administration.
- The half-life and time to onset of action of the two drugs need to be considered when converting so that the patient does not experience breakthrough pain or receive too much opioid during the conversion period.
- In most cases, when switching between different opioids, the calculated dose-equivalent must be reduced to ensure safety with the starting being the calculated equi-analgesic dose of around 50%.
- Conversion factors are an approximate guide only because comprehensive data are lacking, and there is significant inter-individual variation.
- Once the conversion has occurred, the dose of the new opioid should be titrated carefully according to individual response, and the patient should be monitored closely for side effects and efficacy, especially when switching at high doses.
- Withdrawal symptoms (eg, sweating, yawning and abdominal cramps, restlessness, anxiety) occur if an opioid is stopped/dose reduced abruptly.
Approximate equi-analgesic potencies of opioids for oral administration
(Reviewed August 2020 to reflect current BNF figures)
| Medication | Potency | Equivalent dose to 10mg oral morphine |
|---|---|---|
| Codeine phosphate | 0.1 | 100mg |
| Dihydrocodeine | 0.1 | 100mg |
| Hydromorphone | 5 | 2mg |
| Methadone | * | * |
| Morphine | 1 | 10mg |
| Oxycodone | 1.5 | 6.6mg |
| Tapentadol | 0.4 | 25mg |
| Tramadol | 0.1 | 100mg |
* The relative potency of methadone depends on the starting dose and the duration of administration. Conversions to and from methadone should always be undertaken with specialist advice
Transdermal Opioids
(Reviewed August 2020 to reflect current BNF figures)
A. Buprenorphine
Transdermal buprenorphine changed at weekly intervals
| Medication | 5 microgram/hr | 10 microgram/hr | 20 microgram/hr |
|---|---|---|---|
| Codeine phosphate (mg/day) | 120mg | 240mg | |
| Morphine sulphate (mg/day) | 12mg | 24mg | 48mg |
Transdermal buprenorphine changed every three or four days (twice weekly)
| Medication | 35 micrograms/hr | 52 microgram/hr | 70 micrograms/hr |
|---|---|---|---|
| Morphine sulphate (mg/day) | 84mg | 126mg | 168mg |
B. Fentanyl
| Fentanyl patch strength (microgram/hr) | Oral morphine (mg/day) |
|---|---|
| 12 | 30 |
| 25 | 60 |
| 50 | 120 |
| 75 | 180 |
| 100 | 240 |