Intravenous Opioid Dose Titration for Refractory Cancer Pain: A Comparative Analysis of Switching from Transdermal Fentanyl to Morphine or Methadone

INTRODUCTION: Switching from transdermal fentanyl (TDF) to other opioids is clinically challenging because of the subcutaneous reservoir that delays drug elimination. This study compares the efficacy and safety of intravenous (IV) dose titration with morphine (MO) versus methadone (ME) as a "bridging" strategy to overcome this pharmacological lag. METHODS: In this secondary analysis of an observational cohort study, patients who required an opioid switching from TDF (≥ 50 µg/h) to IV morphine or IV methadone were selected. As per protocol of the original study, patients were titrated with IV boluses of MO (n = 17) or ME (n = 22) until analgesia was achieved, followed by continuous infusion and subsequent oral conversion. The primary outcome was clinical stabilization; secondary outcomes included the comparison of final oral morphine equivalents (OME). RESULTS: Both groups achieved analgesia rapidly. The median IV dose required for stabilization was 10 mg for MO and 15 mg for ME (p = 0.152). Methadone demonstrated a significant "opioid-sparing" effect, allowing stabilization with equianalgesic doses (OME) significantly lower than those used in the morphine group and compared to baseline TDF. CONCLUSION: IV opioid dose titration is a safe and effective method for managing TDF switching effectively eliminating the "waiting period" associated with patch removal. While both drugs are effective, methadone stands out for its ability to significantly lower the total daily opioid requirement.