Inadequate Cancer Pain Control after Switching High-Dose Fentanyl to Hydromorphone Injection: A Case Series Highlighting Issues with Conventional Conversion Ratios.

Opioid conversion, particularly from high-dose intravenous (IV) fentanyl (>120 mg/day oral morphine-equivalent daily dose per referenced Japanese guidelines) to IV hydromorphone, presents clinical challenges due to inconsistent conversion ratios and lack of robust evidence. Specific approaches used in Japan may require careful evaluation. This report details two advanced cancer patients experiencing inadequate pain control after switching from high-dose IV fentanyl to IV hydromorphone. Conversions were based on calculations reflecting common Japanese practice. In both cases, pain worsened significantly, necessitating reversion to the original fentanyl regimen to regain acceptable analgesia. Conventional fentanyl-to-hydromorphone conversion ratios applied in Japan may underestimate the required hydromorphone dose when switching from high fentanyl baselines, risking therapeutic failure. These cases highlight the need for caution, consideration of potentially higher initial hydromorphone doses, close monitoring, and individualized strategies, including reverting to the prior opioid, for this specific rotation, especially in high-dose scenarios.