Serum concentrations of lidocaine and its metabolites after prolonged infusion in healthy horses.

The research article shows how the serum concentrations of lidocaine and its metabolites behave when administered to healthy horses over a sustained period. The study demonstrated that while lidocaine metabolism was not significantly impaired, the accumulation of glycinexylidide could be a potential concern.

Objective and Methods

• The main goal of this study was to examine the time and concentration relationship of lidocaine and its two active metabolites — glycinexylidide (GX) and monoethylglycinexylidide (MEGX)— given to horses over a period of 96 hours through continuous-rate infusions (CRIs).
• This represents a significant extension of previous studies, which only examined lidocaine administration over a shorter 24-hour period.
• Eight mature, healthy horses were administered lidocaine at a continuous rate infusion for 96 hours, and blood concentrations of lidocain and its metabolites were monitored using high performance liquid chromatography both during the infusion and after discontinuation.

Results

• The serum lidocaine concentrations in the horses reached a steady state by the third hour and didn’t accumulate beyond this point.
• The concentrations were above the targeted therapeutic concentration only at two points – six and 48 hours, without reaching toxic levels at any point.
• While MEGX didn’t accumulate over time, GX showed significant accumulation up to the 48-hour mark, after which it remained constant.
• All detectable concentrations of lidocaine, MEGX, and GX disappeared from the horses’ systems within 24 hours of discontinuation of the infusion.
• None of the horses displayed any signs of lidocaine toxicity throughout the study.

Conclusions

• Long-term infusions of lidocaine didn’t significantly impair lidocaine metabolism and didn’t lead to any adverse effects, thus proving to be safe for normal, healthy horses.
• The notable accumulation of GX, however, was identified as a potential concern due to its potentially toxic effect, bringing to attention the need for careful monitoring during such treatments.