Pharmacokinetics of enrofloxacin in horses after single intravenous and intramuscular administration.

The study is about understanding how the drug enrofloxacin behaves in the body of horses when administered either intravenously or intramuscularly, the potential side effects of the drug, and its effectiveness in circulating within the horse body.

Research Purpose and Procedure

• The objective of the research was to assess the pharmacokinetics—the way the body absorbs, distributes, metabolizes, and excretes a drug—of the veterinary antibiotic enrofloxacin when injected into horses either through the veins (intravenously) or into the muscles (intramuscularly).
• The study used 6 horses and administered enrofloxacin at a dosage of 5 mg/kg body weight. The concentrations of enrofloxacin and its metabolite, ciprofloxacin, in the horses’ blood serum were measured using high performance liquid chromatography, a method used to identify and quantify components in a mixture.
• Reactions at the injection site were also monitored both clinically (through physical observation) and through the determination of serum creatine kinase (CK) activity, an enzyme whose increased levels can indicate muscle damage.

Findings of the Research

• Following intravenous administration, the drug had an elimination half-life—the time it takes for the drug’s concentration in the body to reduce by half—of about 4.4 hours and its distribution volume within the body was 2.3 liters per kilogram of body weight.
• The drug was found to be quickly metabolized into ciprofloxacin, and the half-life of this metabolite paralleled that of the original drug. The concentration of ciprofloxacin in the serum reached 20-35% of that of the initial drug.
• However, when administered intramuscularly, the elimination half-life of the drug was longer, at 9.9 hours, and the time taken for the drug to be absorbed was also found to be long, at the same duration.
• When comparing the half-life and mean residence time—the average time a molecule stays in the body—no significant differences were found between the antimicrobial activity of enrofloxacin and ciprofloxacin.
• Interestingly, intramuscular injection of enrofloxacin was found to cause significant irritation. This was evident from the sharp increase in CK enzyme activity in the serum, which was more than 10 times its level before injection, and it remained high during the 32-hour follow-up period.
• Clinical reactions were observed in two out of six horses, exhibited by swelling and tenderness at the injection site.