Switching to Intravenous Methadone in Advanced Cancer Patients: A Retrospective Analysis

Abstract

Context: Information about opioid switching to intravenous methadone is lacking. Objectives: The aim of this study was to assess the outcome of opioid switching to intravenous methadone (IV-ME) in patients admitted to an acute supportive/palliative care unit (ASPCU). The secondary outcome was to assess the conversion ratio from IV-ME to oral methadone at time of hospital discharge. Methods: We retrieved from the pharmacy registry the list of patients who were prescribed IV-ME during their ASPCU admission for a period of 47 months. Poor analgesia with previous opioids and/or adverse effects were the main indications for opioid switching. IV-ME was titrated until acceptable analgesia was achieved. The effective dose was multiplied by three to establish the intravenous daily dose, given as a continuous infusion. Doses were then changed according to the clinical needs. Once the patient was stabilized, IV-ME dose was converted to oral methadone, by using an initial ratio of 1:1.2. Further dose changes were made according to clinical needs until stabilization, before patients' discharge. Information about patients' characteristics, pain scores on the Edmonton Symptom Assessment Scale (ESAS), Memorial Delirium Assessment Scale (MDAS), Cut-down, Annoyed, Guilty, Eye-opener (CAGE) questionnaire, previous opioids and their doses, expressed as oral morphine equivalents (OME), were recorded. The effective bolus of IV-ME, initial daily infusion rate, and oral methadone doses were assessed, and conversion ratios calculated. Results: Forty-one patients were taken into consideration for the study. The mean effective bolus of IV-ME titrated for achieving acceptable analgesia was 9 mg (range 5-15 mg). The mean daily continuous infusion rate of IV-ME was 27.6 mg/day (SD 21). The mean daily dose of oral methadone at time of discharge was 46.8 mg/day (SD 43). Discharge occurred within a median of seven days (range 6-9) after admission. Previous opioid (OME)/IV-ME, oral-IV-ME, and previous opioid (OME)/oral methadone were 6.25, 1.7, and 3.7, respectively. Conclusion: IV-ME dose titration followed by intravenous infusion allowed a rapid pain control in few minutes in patients with severe pain intensity, not responsive to previous opioids. Conversion to oral route was successful and facilitated home discharge. Further studies should be performed to confirm these preliminary results.