Information about equi-analgesic doses of methadone have been removed from 'Table 1: Equipotency of opioid analgesics to oral morphine 30 mg', in the Dosing Issues section of this NPS RADAR review published in the August 2006 issue.
Although based on information provided in the product information, subsequent expert advice suggests that methadone has a much greater potency compared with morphine than the doses described in the Durogesic product information.1 In single-dose studies in opioid-naïve patients, methadone is 1-2 times as potent as morphine, but its potency in long-term use may be 10 times greater than morphine.2,3 Prescribers are advised to consult a pain management specialist if considering switching a patient from oral methadone to fentanyl patches.
When switching from any opioid to fentanyl patches, remember that dose conversions are estimates often based on single-dose studies and that dose-conversion ratios are a function of previous opioid exposure. There can be substantial individual variation in response.
- Janssen-Cilag Pty Ltd. Durogesic transdermal system product information. 9 Dec 2005.
- Analgesic Writing Group. Therapeutic Guidelines: Analgesic. Version 4. North Melbourne: Therapeutic Guidelines Pty Ltd, 2002.
- Schug SA, Gandham N. Opioids - Clinical Use. In: McMahon S, Koltzenburg M, eds. Wall and Melzack's Textbook of Pain. 5th edn. London: Elsevier, 2005.