Objectives To assess the physicochemical stability of the combination of a propofol emulsion with an alpha-2 (α2) adrenergic receptor agonist (α2A; clonidine or dexmedetomidine) under conditions mimicking routine practice in an intensive care unit or in multimodal analgesia procedures.

Methods We developed and validated three stability-indicating methods based on high-performance liquid chromatography with ultraviolet (HPLC-UV) detection. Eight different conditions per combination were evaluated in triplicate, with variations in the simulated, bodyweight-adjusted dose level and the drugs’ flow rate. The drugs were mixed in clinically relevant concentrations and proportions and then stored unprotected from light, in clear glass vials at room temperature for 96 hours. At each sampling point, we assessed the chemical stability (the HPLC-UV drug level, pH, and osmolality) and physical compatibility (visual aspect, zeta potential (ZP), mean droplet diameter (MDD, Z-average) and polydispersity index (PDI)). We validated our stability findings in positive and negative control experiments.

Results Over the 96-hour test, the concentrations of propofol, clonidine and dexmedetomidine did not fall below 90% of the initial value, and the pH and osmolality were stable. The visual aspect of the mixed propofol emulsions did not change. The MDD remained below 500 nm (range 165–195 nm). The PDI was always below 0.4; 78.7% of the measurements were below 0.1 and 21.3% were between 0.1 and 0.4. The ZP measurements (−31.3 to −42.9 mV) suggested that the emulsion was stable. The MDD and PDI increased slightly at 96 hours under some conditions, which might indicate early destabilisation of the emulsion. Given that the MDD remained below 500 nm, these emulsions are compatible with intravenous administration.

Conclusions Our results demonstrate the chemical and physical compatibility of propofol-α2 agonist mixtures at concentrations and in proportions representative of standard protocols when stored unprotected from light at room temperature for 96 hours.