Background. The aim of this study was to retrospectively review the chart of cancer patients switched to methadone for unfavorable response to the previous opioid.
Methods. Retrospective reviewed consecutive medical records of patients undergoing opioid switching to methadone were evaluated. Patients who were switched from different opioids to methadone, because of poor pain relief in the presence of adverse effects limiting further dose increases despite symptomatic treatment, were selected. After the initial oral dose, the subsequent doses were flexible and were changed timely to fit the patients' needs in an attempt to find the best balance between pain and opioid-related symptoms.
Results. Three hundred forty-five patients underwent switching to methadone. Twenty-seven patients were not considered feasible for analysis. Only one patient required the use of naloxone for the occurrence of bradypnea. A total of 77.4% substitutions for methadone were considered successful. The median time to achieve daily dose stabilization in patients successfully switched was 3 days. Fifty-one substitutions failed. For all previous opioids, no significant differences between initial conversion ratios and ratios achieved after stabilization were found (P = 0.42). No significant correlation between the previous opioid dose and the final conversion ratio was found (P = 0.19).
Conclusions. Switching to methadone from different opioids, using an initial fixed ratio followed by a flexible dosing, according to the clinical need, is highly effective and safe when performed in an acute pain relief and palliative care unit. Further studies should assess this approach in other settings.