Pharmacokinetics of marbofloxacin in mature horses after single intravenous and intramuscular administration.

The research study tested the absorption, distribution, metabolism, and excretion of marbofloxacin – a fluoroquinolone antimicrobial agent – under specific conditions in horses. They found that the drug demonstrates a high volume of distribution, suggesting effective penetration into tissues, and it also shows a prolonged half-life, indicating slower elimination from the body.

Study Design

• The research investigated the pharmacokinetic characteristics of a new fluoroquinolone antimicrobial agent marbofloxacin in mature horses.
• Marbofloxacin was given in a single dose, intravenously (i.v) and intramuscularly (i.m), at a dosage strength of 2 mg/kg.
• The concentration of the drug in the plasma were derived through a technique known as high-performance liquid chromatography (HPLC).
• The data obtained from the study were subjected to compartmental and noncompartmental kinetic analysis.

Results and Findings

• Marbofloxacin demonstrated a high volume of distribution (about 1.17 liters per kilogram), suggesting good penetration into the body tissues.
• The total clearance (Cl) rate of the drug was recorded as 0.19 liters per kilogram per hour. This means that the drug was relatively slowly eliminated from the body, as indicated by its long half-life duration.
• The drug was rapidly absorbed after being adminstered intramuscularly with 87.9% bioavailability. No significant difference was noted between the intravenous and intramuscular routes in terms of pharmacokinetic parameters.
• No adverse reactions were observed at the site of injection when marbofloxacin was administered intramuscularly to horses. However, the researchers recorded a rise in CK activity, a marker for muscular damage, after 12 hours of drug administration. But the activity decreased within the following 24-hour period.
• Based on the ability of the drug to reach a required concentration to inhibit pathogenic microorganisms (MIC), the researchers concluded that a single daily dose of 2 mg/kg may not be effective in treating infections caused by pathogens with an MIC of 0.25 micrograms per milliliter or higher. Conversely, using traditional antimicrobial efficacy criteria, marbofloxacin attains high plasma concentration and maintains levels higher than MICs established against most gram-negative veterinary pathogens.
• The study recommends a single daily dose of 2 mg/kg, considering that fluoroquinolones are believed to have concentration-dependent effects and long post-antibiotic effects against gram-negative bacteria.