Disposition of enrofloxacin in plasma, pulmonary epithelial lining fluid, peritoneal fluid, and cerebrospinal fluid of healthy mares.

This study aimed to investigate how the drug enrofloxacin and its active metabolite, ciprofloxacin, are distributed in the bodies of healthy mares. It found that enrofloxacin at a higher dosage achieved higher concentrations and more prolonged presence in fluid matrices, although no pharmacokinetic advantage was noted for susceptible isolates.

Study Methodology and Process

• The researchers involved in this study performed their experiments on 6 healthy, mature mares. These mares were selected randomly to receive a single dose of enrofloxacin at either 5 mg/kg or 7.5 mg/kg.
• The experiment was designed as a crossover, which means each horse received both dosages with a washout period of 10 days. The washout period is a phase of the experiment where the subjects are cleansed of the drug to eliminate any residual effects that might be present during subsequent dosage periods.
• The concentration levels of both enrofloxacin and ciprofloxacin were subsequently measured in four biological fluids: plasma, pulmonary epithelial lining fluid (PELF), peritoneal fluid, and cerebrospinal fluid (CSF).

Findings of the Study

• The researchers noted that both doses of enrofloxacin were generally well tolerated by the horses, with one horse showing signs of focal, self-limiting limb edema.
• They found that certain pharmacokinetic parameters of enrofloxacin – such as the median maximum concentration and area under the plasma concentration-versus-time curve – were significantly higher in the plasma of horses that were given the higher dose (7.5 mg/kg). Pharmacokinetic parameters relate to how the body metabolizes and excretes a drug, affecting its concentration in the body over time.
• Contrarily, there were no considerable variations in the pharmacokinetic variables measured in PELF between the two different dosage groups. Thus, the PELF did not show any concentration advantage for the higher dosage of enrofloxacin.
• Although the 7.5-mg/kg dose resulted in higher concentrations and displayed more extended persistence in fluid matrices, it did not present a clear pharmacokinetic advantage for susceptible isolates. Further studies are recommended to understand whether the higher concentration and the prolonged persistence are clinical advantages.

Significance of the Study

• This study provides valuable pharmacokinetic data for the use of enrofloxacin in horses, which has been lacking. Such data can help veterinarians make more informed decisions regarding the dosage and administration frequency of this drug.
• Despite enrofloxacin’s widespread usage, there is limited understanding of its behavior in the equine body. This study contributes to filling this gap in knowledge and could direct the design of future studies to fully comprehend enrofloxacin’s impacts on horse health.