Background: Methadone is increasingly being used to treat patients whose pain does not respond well to other opioids. Advantages over morphine sulphate and its alternatives include low cost, lack of active metabolites and efficacy against neuropathic pain.

Objective: To describe our experience with opioid rotation to methadone and compare the morphine to methadone ratios to previously published data; To discuss two commonly used rotation methods--the Edmonton and Morley-Makin methods.

Methods: We describe two cases with cancer pain successfully switched to methadone. In both cases the dose of the previous opioid was limited by development of opioid toxicity. We used the Morley-Makin conversion method and modified it by reducing the 'as required' dose by a third. The initial methadone doses for these cases were lower than predicted doses.

Conclusions: In cases where cancer patients fail to respond or develop tolerance to opioids, conversion to methadone is a reasonable approach. Although equianalgesic tables may not always predict final methadone doses, when properly selected can be useful tools for the experienced clinician. A customised and cautious approach is thus advisable when rotating to oral methadone, especially in patients who have experienced opioid toxicity.