Rapid switching from morphine to methadone in cancer patients with poor response to morphine

Purpose: The aim of this study was to evidence the clinical effects of an abrupt substitution of morphine with methadone using a fixed ratio of 1:5 in patients for whom limiting adverse effects occurred before adequate analgesia was achieved with oral morphine. Patients and Methods: A cross- sectional prospective study was carried out on 24 consecutive patients who were switched from oral morphine to oral methadone because they experienced substantial adverse effects that limited further increase in morphine dose. A fixed conversion morphine-to-methadone ratio of 5:1 was chosen. Subsequently, doses were changed according to clinical need, with frequent visits or phone contacts. Pain and symptom intensity, preswitching doses of morphine, initial and subsequent doses of methadone, and survival were recorded. Results: A significant decrease in pain and symptom intensity was found within 24 hours after the substitution took place. The switching was effective in most patients (19 of 24), although five patients required alternative treatments. No significant changes in methadone dose were reported in the 3 days after switching. Methadone dose was significantly higher in patients who had lower preswitching doses of morphine and vice versa. No relevant complications were reported. Conclusion: A rapid substitution of morphine with methadone using an initial fixed ratio of 5:1 is a safe and effective method for improving the balance between analgesia and adverse effects in cancer patients with poor morphine response. An appropriate system of patient monitoring is necessary, because further changes in dose may be required according to clinical needs.