Effect of xylazine and ketamine on the pharmacokinetics of alfentanil during halothane anaesthesia.

The study investigates the pharmacokinetics, or how the body absorbs, distributes, metabolizes, and excretes a drug, of alfentanil in horses under different types of anesthesia. The researchers note that the way alfentanil behaves changes depending on whether halothane, xylazine, or ketamine is used for anesthesia.

Research Methodology

The researchers conducted a study involving:

• two horses,
• each of which underwent three different tests, which were administered in a random order.

In each test, the horses received anesthesia via a mask, followed by a dose of alfentanil either as a single shot (a “bolus” dose) or as an infusion over 120 minutes. In one of the tests, the anesthesia was supplemented with xylazine and ketamine.

Analyzing the Data

• The scientists measured the concentration of alfentanil in the horses’ blood over time, noting how the concentration changed as the drug was processed by the body.
• They mapped these changes, creating plasma concentration-time curves.
• In the tests where the horses received only halothane anesthesia, these curves could be described using a “two-compartment open model”, a mathematical model that describes how a drug is distributed in and removed from the body.

Findings and Conclusion

• However, when the researchers looked at the data from the test where xylazine and ketamine were used, they observed a steady level – a “plateau” – in the plasma concentration-time curve.
• This curve didn’t fit their two-compartment model, suggesting that something else was happening when the horses received this combination of drugs.
• They propose that a “three-compartment open model” with an additional component that describes extra drug input might be a better fit for the data when xylazine and ketamine given in addition to the halothane anesthesia.
• The additional component is likely to be a result of how the combination of xylazine and ketamine affects the body’s processing of alfentanil.