Pharmacokinetic profile in relation to anaesthesia characteristics after a 5% micellar microemulsion of propofol in the horse.

This study investigates the pharmacokinetic behaviour of a 5% micellar microemulsion formulation of propofol in horses. It tries to correlate the propofol plasma concentrations with anesthetic characteristics in horses to inform about its safe usage in equine anaesthesia.

Research Methodology

• The experiment was first carried out on six xylazine-sedated horses by giving them a bolus (large volume) injection of propofol administered in a defined dosage of 2 mg per kg.
• After the initial bolus, a dosage of 8.1 (standard deviation 3.2) mg per kg per hour of propofol was continuously infused into the same six horses for a period of three hours.
• Further, propofol sold commercially was used on two horses for comparative analysis.
• Venous blood samples were collected periodically from the horses to measure the plasma concentration of propofol, using liquid chromatography-mass spectrometry, a technique that separates and identifies the components of a mixture.
• The horse’s response to noxious stimulation (painful stimuli) was used to evaluate the analgesic effectiveness of propofol.

Results and Observations

• The pharmacokinetic profile of propofol best fits a non-compartmental model, which describes the behaviour of drugs in the body without assuming it’s partitioned into compartments.
• Mean measurements of pharmacokinetic parameters such as the area under the plasma concentration-time curve (measuring the total drug exposure over time), elimination half-life of propofol (time it takes for half of the drug to be eliminated from the body), mean residence time (average time the drug spends in the body), and clearance rate (rate at which the drug is removed from the body) were calculated.
• There was a correlation found between the plasma concentration of propofol and the infusion rate, but this was weak (represented by r-square value of 0.47).
• Most propofol infusion rates didn’t prevent the response to noxious stimulation, meaning they didn’t provide sufficient pain relief. Higher doses led to involuntary muscle contractions.
• Lower plasma propofol concentrations yielded better recovery and the concentration often increased when horses woke from anaesthesia.

Conclusions

• The study concluded that careful administration of the propofol should be adhered to due to variable kinetics, the potential of inducing unwanted muscle activity, insufficient pain relief, and less desirable recovery quality.