Background Alfentanil is a strong short acting synthetic opioid which is increasingly used in specialist palliative medicine. There is uncertainty and pragmatism in determining a conversion ratio from other strong opioids to alfentanil. Subcutaneous diamorphine: subcutaneous alfentanil 10:1 was initially used.¹ Recent retrospective chart reviews suggest that this conversion ratio is conservative, although there are conflicting findings in the literature.^2,3,4 These reviews have focused on converting to alfentanil from diamorphine rather than from opioids more commonly used in clinical practice. This retrospective chart review focuses on switching from oxycodone to alfentanil.

Method A retrospective chart review of consecutive hospice inpatients prescribed alfentanil via continuous subcutaneous infusion was undertaken. Patients were identified using controlled drug books. Data pertaining to demographics, primary diagnosis, renal function, indication for alfentanil rotation, opioid use in the 24 hours prior to rotation, initial alfentanil dose, subsequent dose escalation and reason for stopping alfentanil were collected. Ethical approval was obtained prior to commencement.

Results Data were collected for 20 consecutive inpatients. 90% (18/20) had a primary cancer diagnosis. 50% (10/20) had an eGFR <30mL/minute. As per available data, 83% (15/18) patients were prescribed a regular strong opioid prior to alfentanil switch. Of the 10 patients switched from oxycodone to alfentanil, a conversion ratio of oxycodone (subcutaneous): alfentanil (subcutaneous) of 10:1 was used for 6 patients to determine the initial alfentanil dose (Day 0). 5 of these patients required a dose increase on Day 2, as did the 1 patient with Day 2 data available for whom a conversion ratio of >10:1 was used. A ratio of <10mg:1mg was used for 2 patients, who also required increased doses on Day 2.

Conclusion These findings suggest that a conversion ratio of 10mg oxycodone (subcutaneous):1mg alfentanil may be conservative. This needs further evaluation.

References

1. Kirkham SR, Pugh R. Opioid analgesia in uraemic patients. Lancet. 1995;345:1185.

2. Urch CE, Carr S, Minton O. A retrospective review of alfentanil use for pain in the palliative care setting. Pall Med 2014;28.

3. Virani F, Miller M. Alfentanil in inpatient palliative medicine: practice survey. BMJ Supportive and Palliative Care 2021;0:1–2.

4. Cran A, Dorman S, Kirkham S. Opioid rotation to alfentanil: comparative evaluation of conversion ratios. BMJ Support Palliat Care 2017;7:bmjspcare-2017–001349-266.