Influence of gastrointestinal tract disease on pharmacokinetics of lidocaine after intravenous infusion in anesthetized horses.

This study investigates how the presence of gastrointestinal disease in horses affects the pharmacokinetics of lidocaine, a common anesthetic, when delivered via intravenous infusion. The researchers tracked the serum lidocaine concentrations and several cardiopulmonary variables in horses undergoing exploratory laparotomy, with the results intended to inform optimal dosing practices for horses with digestive issues.

Methodology

• The study involved eleven horses, with an average age of approximately 10.3 years, weighing around 526 kg each.
• Each horse was given a dose of lidocaine hydrochloride – a loading infusion of 1.3 mg/kg over a 15-minute duration, followed by a maintenance infusion at 50 microg/kg/min for 60 to 90 minutes.
• The horses were in a state of dorsal recumbency (lying on their back) under anesthesia during the administration of lidocaine.
• Blood samples were collected at different time intervals before, during, and after the lidocaine infusion. These samples were used to measure serum lidocaine concentrations via advanced laboratory techniques, namely liquid chromatography-mass spectrometry.
• The data from these measurements were analyzed using standard noncompartmental pharmacokinetic techniques.

Measurements and Observations

• Key cardiopulmonary variables were monitored and recorded, such as heart rate (HR), mean arterial pressure (MAP), arterial pH, partial pressure of carbon dioxide (PaCO2), and oxygen saturation (PaO2).
• The quality of recovery from anesthesia was also assessed and recorded, ranging from poor to excellent.

Results

• The study found that the serum lidocaine concentrations increased dramatically with the initiation of the loading infusion and decreased sharply following the discontinuation of the maintenance infusion.
• The volume of distribution of lidocaine at a steady-state was found to be 0.70 L/kg, while total body clearance and the half-life of the drug were recorded to be 25 mL/kg/min and 65 minutes, respectively.
• The values of the cardiopulmonary variables were within the standard range for anesthetized horses. The mean HR ranged from 36 to 43 beats per minute, and the mean MAP oscillated between 74 and 89 mm Hg.

Conclusions

• The researchers concluded that these findings will contribute to the availability of pharmacokinetic data, which is crucial for determining the appropriate clinical dosage of lidocaine in horses suffering from gastrointestinal tract diseases.
• With these insights, veterinarians can adjust their lidocaine dosing strategies to ensure optimal safety and efficacy when treating such horses.