Background Propofol, a general anaesthetic, and remifentanil, an opioid analgesic, are used to both induce and maintain sedation. They often need to be administered simultaneously via the same venous catheter lumen. This predisposes to potential compatibility issues with undesirable consequences such as catheter obstruction and, ultimately, embolism. Propofol is a fat emulsion and available formulations differ considerably in fat composition. Diprivan contains 100% pure long chain triglycerides (LCT) whereas Propolipid and Propofol-Lipuro contain 50% LCT and 50% medium-chain triglycerides (MCT). The three formulations also differ in the type and amount of other excipients. There is no exhaustive information on all three propofol formulations.

Purpose Our aim was to determine and compare the emulsion stability of propofol formulations Propolipid, Propofol-Lipuro and Diprivan when administered together with remifentanil.

Material and methods To simulate Y-site compatibility, remifentanil (Ultiva) 50 µg/ml was mixed in vials with 10 mg/ml concentrations of Propolipid, Propofol-Lipuro and Diprivan, respectively. The mixing ratios of remifenatnyl:propofol were1:1 and 10:1. Controls consisted of each propofol formulation analysed separately. Analysis was conducted immediately after mixing and 4 hours’ later. Emulsion stability was determined by calculating the percentage of fat residing in globules larger than 5 µm (PFAT5), measuring pH and mean droplet diameter.

Results None of the propofol formulations resulted in increased PFAT5 immediately after mixing with remifentanil in mixing ratios of 1:1 and 10:1. However, all formulations resulted in PFAT5 levels over what is acceptable 4 hours’ after mixing with remifentanil except for Propolipid and Diprivan in mixing ratio 1:1. No difference in mean droplet diameter was noticed and we did not see an association between the decreased pH that occurred and the stability of the emulsions.

Conclusion Remifentanil administered with propofol formulations in the same intravenous catheter may lead to emulsion instability. If the infusion rate is slow, separate intravenous administration of these drugs should be considered.

References and/or acknowledgements No conflict of interest.