Background Methadone can be used to treat complex or neuropathic pain. Due to its unique pharmacological properties, switching from another opioid is complex. Ratios and equianalgesic doses are a consequent challenge for physicians, with no standardised ratios in use.
Aims/Objectives To compare a novel method of methadone rotation with other commonly used methadone conversion methods including Perth rapid titration, Brisbane protocol and 3-day switch.
Ethical approval was obtained A retrospective chart review of all inpatients prescribed methadone during 2018/2019 was conducted. Data collected included demographics, opioid requirement prior to rotation and oral morphine equivalent (OME), presence of opioid toxicity, opioid-sparing interventions, final stable methadone dose prescribed, time to achieve stable dose. Stable methadone dose was defined as a dose that was stable for 5 days or until death/discharge. Using the OME, the expected methadone dose was calculated via rapid titration with both the Perth protocol and ‘Brisbane’ Protocol, as well as 3-day switch. This data was compared with the results of our study.
Results 86 charts were identified, 9 were not located, 49 were excluded including methadone use as an adjunct and discontinuation of rotation. 28 rotations were analysed. The mean methadone dose was 12.6 mg using this novel method. Calculated methadone doses with Perth protocol were significantly higher than doses achieved using this novel method of rotation, with a mean difference of 13.9mg (p value <0.0001). Calculated doses were also higher when comparing the Brisbane method and this novel method, mean difference noted to be 4.6mg (p value 0.0035). No statistically significant difference was found when comparing with the 3-day switch.
Conclusion Patients rotated to methadone using this novel method received a stable methadone dose lower than they may have received if Perth or Brisbane ratio conversions were used. Methadone rotation remains challenging and further study is needed.
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