Pharmacokinetics of marbofloxacin in mature horses after single intravenous and intramuscular administration.
Authors: Carretero M, Rodríguez C, San Andrés M I, Forés P, de Lucas J J, Nieto J, Waxman S, San Andrés M D, González F
Journal: Equine veterinary journal
Summary
Marbofloxacin, a veterinary-exclusive fluoroquinolone, was evaluated in five mature horses to characterise its absorption and elimination following intravenous and intramuscular dosing at 2 mg/kg, with plasma concentrations measured by HPLC and subjected to compartmental analysis. The drug demonstrated favourable tissue distribution properties (volume of distribution 1.17 l/kg) and prolonged elimination (half-life approximately 4.7–5.5 hours), with rapid intramuscular absorption (33.8 minutes) and excellent bioavailability of 87.9%, meaning practitioners can expect comparable clinical outcomes regardless of administration route. Whilst mild elevation of serum creatine kinase occurred at 12 hours post-intramuscular injection, this resolved within 24 hours without local adverse effects, and no significant pharmacokinetic differences were observed between routes. For practitioners selecting dosing regimens, the concentration-dependent bactericidal activity and prolonged postantibiotic effect characteristic of fluoroquinolones support a once-daily 2 mg/kg protocol against susceptible organisms; however, infections caused by pathogens with minimum inhibitory concentrations of 0.25 μg/ml or higher may require dose escalation or increased dosing frequency to achieve adequate pharmacodynamic targets. These findings provide evidence-based guidance for integrating marbofloxacin into equine treatment protocols, particularly where rapid antimicrobial activity and tissue penetration are clinically advantageous.
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Practical Takeaways
- •Marbofloxacin at 2 mg/kg IM once daily is well-absorbed with minimal injection site reactions and long tissue residence time, making it practical for field use
- •Efficacy depends on pathogen susceptibility; confirm MIC values before use as some gram-negative pathogens may require higher doses or more frequent administration
- •The long half-life and good tissue penetration suggest this fluoroquinolone may achieve therapeutic concentrations in infected tissues despite modest plasma levels
Key Findings
- •Marbofloxacin shows high volume of distribution (1.17 ± 0.18 l/kg) indicating good tissue penetration in horses
- •Elimination half-life is long (4.74-5.47 hours) supporting once-daily dosing intervals
- •Intramuscular absorption is rapid (MAT 33.8 ± 14.2 min) with high bioavailability of 87.9 ± 6.0%
- •A dose of 2 mg/kg every 24 hours may be inadequate against pathogens with MIC ≥0.25 µg/ml based on PK/PD targets