Characterization of the pharmacokinetic disposition of levofloxacin in stallions after intravenous and intramuscular administration.

This study examined how the drug levofloxacin behaves in the body of stallions (male horses) after being administered via intravenous or intramuscular injection. The research indicates that levofloxacin could potentially have a good therapeutic profile for treating both Gram-negative and Gram-positive bacterial infections in horses.

Methodology

• The research involved six stallions who were each given a single dose of levofloxacin, either via an intravenous (i.v.) bolus or an intramuscular (i.m.) injection.
• The dose rate was 4 mg/kg of body weight (bwt).
• The experiment was designed as a two-phase crossover study, with a 15-day break between phases.
• Plasma samples were collected at different time intervals over a 48-hour period following the administration of the drug.
• The samples were analyzed with a microbiological assay method to understand the disposition of levofloxacin in the plasma.

Results

• Following the i.v. dose, the plasma disposition of levofloxacin best fitted a two-compartment open model, i.e., the body can be considered as two compartments or areas – central and peripheral – where the drug is contained.
• The half-lives of distribution and elimination – reflecting how quickly the drug spreads and is cleared from the body – were approximately 0.21 hours and 2.58 hours respectively.
• The volume of distribution at steady-state (how much the drug spreads within the body) was approximately 0.81 L/kg.
• The total body clearance was approximately 0.21 L/h/kg.
• The areas under the concentration-time curves (a measure of drug exposure over time) were around 18.79 microg.h/mL for i.v. dosing and 17.21 microg.h/mL for i.m. injection.
• The time it took to reach maximum concentration in the blood following intramuscular injection was roughly 1.56 hours.
• The bioavailability (the proportion of the drug that enters circulation) was high, at 91.76%, implying that most of the administered drug was utilized by the body.
• The protein binding percentage, which indicates how much of the drug attaches to proteins in the blood, was 27.84%.

Implications

• Efficacy predictors suggested that levofloxacin might have a good therapeutic profile against both Gram-negative and Gram-positive bacteria, with a minimum inhibitory concentration (MIC) less than or equal to 0.1 microg/mL. The MIC is the lowest concentration of a drug that prevents growth of a particular bacterium, so a low MIC suggests effective antibacterial action.
• The study furnishes useful baseline data to guide levofloxacin dosing and timetabling in equine treatment regimens.