The disposition of lidocaine during a 12-hour intravenous infusion to postoperative horses.

This research paper studies lidocaine’s effect on horses when it is administered as a 12-hour intravenous infusion, analyzing plasma concentrations and pharmacokinetics, as well as evaluating whether it binds with proteins in the blood.

Objective of the Study

• The primary objective was to evaluate the plasma concentration levels and the pharmacokinetics, which relate to how the body processes the drug, of lidocaine administered to horses for 12 hours post-operation.
• The secondary objective was to investigate how lidocaine binds with plasma proteins in horse blood in a laboratory setting. This understanding is crucial because high-protein-binding drugs can potentially displace lidocaine and increase unbound amounts, which may contribute to toxicity.

Methodology

• Lidocaine hydrochloride was administered to six postoperative horses at a specified dose and then by a constant rate of IV infusion.
• Lidocaine plasma concentrations were measured consistently using a high-pressure liquid chromatography method which helps in the analysis of the molecular components of a mixture.

Results

• Throughout the investigation, one of the horses experienced tremors and collapsed around 5.5 hours into the study, hinting at a potential adverse effect of the treatment.
• The range of lidocaine plasma concentrations during the infusion was observed to be between 1.21-3.13 microg/mL.
• Lidocaine plasma concentrations were significantly higher at multiple intervals compared to the initial hours of the study.
• The in vitro study revealed that lidocaine binds moderately with proteins in horse plasma. This binding decreased when lidocaine was used in combination with ceftiofur, an antibiotic, or the combination of ceftiofur and flunixin, a nonsteroidal anti-inflammatory drug.

Conclusion

• The observations suggest that a lower lidocaine infusion rate might be safer for horses receiving long-term lidocaine infusions due to potential adverse effects.
• The research also unveiled that lidocaine has a moderate binding affinity with proteins in equine plasma. However, the introduction of certain drugs could reduce this affinity, potentially increasing the unbound concentrations of lidocaine and the risk of lidocaine toxicity.