Background The evidence base surrounding conversion of high dose alfentanil to oxycodone via continuous subcutaneous infusion (CSCI) is limited. This case report aims to contribute to this. A lady in her 50s with a uterine leiomyosarcoma developed intra-abdominal sepsis secondary to a large mesenteric mass while in an acute hospital. The sepsis precipitated morphine sulphate toxicity and acute kidney injury prompting opioid rotation to alfentanil via CSCI and prn oxycodone. Escalation of abdominal pain during subsequent hospice admission necessitated titration of alfentanil to 28 mg/24 hours. Persistent pain scores of greater than or equal to 6 on the symptom assessment scale (SAS) over 3 consecutive days when alfentanil was titrated from 24 mg to 28 mg, suggested higher doses were not conferring additional analgesic benefit.
Management Rotated to oxycodone via CSCI to manage persistent severe pain. Renal impairment resolved at this time. 28 mg subcutaneous alfentanil estimated as 840 mg oral morphine sulphate equivalent (1 mg injectable alfentanil: 30 mg oral morphine sulphate). Using conversion factor of 1.5:1 estimated as approximately 560 mg oral and 280 mg subcutaneous oxycodone. Considering inter-individual variation, limited evidence and incomplete cross-tolerance; for safety, the dose of oxycodone was reduced by 50%. A CSCI with oxycodone 140 mg was commenced over 24 hours resulting in significant analgesic benefit with a SAS score of 0 (pain) in the succeeding two days. Use of prn analgesia was reduced and no opioid toxicity was observed. No other medicines were adjusted.
Discussion This is consistent with anecdotal evidence that the analgesic efficacy of alfentanil wanes at doses >20 mg/day possibly indicating tolerance. Admittedly, alfentanil was titrated in small increments in the days preceding rotation. Half the estimated equivalent oxycodone dose conferred analgesic benefit supporting significant dose reduction when rotating.
Conclusion This case describes improved analgesic efficacy despite 50% dose reduction when converting high dose alfentanil to oxycodone via CSCI.
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