The Influence of Age on the Pharmacokinetics of Enrofloxacin and Ciprofloxacin in Calves

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Abstract
This study investigated age-related variations in the pharmacokinetics of enrofloxacin and its active metabolite, ciprofloxacin, in calves. This study was carried out on a total of 18 calves using a parallel pharmacokinetic design. Eighteen animals were assigned to three age groups, one, four, and eight months old, and received a single intravenous dose of 10 mg/kg enrofloxacin. Serial blood samples collected over 48 h were analyzed using high-performance liquid chromatography to determine plasma concentrations. In one-month-old calves, the pharmacokinetic parameters revealed a volume of distribution at steady state (Vdss) of 1.44 L/kg, total clearance (ClT) of 0.42 L/h/kg, elimination half-life (t1/2ʎz) of 2.52 h, and area under the concentration versus time curve (AUC0-last) of 23.36 h*μg/mL. Notably, the AUC0-last of enrofloxacin was increased and ClT decreased in the older age groups (four and eight months). Additionally, the Vdss of enrofloxacin significantly decreased in eight-month-old calves relative to younger groups, while t1/2ʎz showed statistically significant differences in the order of four months > eight months > one month. The conversion ratio of enrofloxacin to ciprofloxacin was highest in one-month-old calves (43.39%) and diminished in four-month-old (25.73%) and eight-month-old (23.04%) calves. The results indicated that the pharmacokinetics of enrofloxacin and ciprofloxacin at a dose of 10 mg/kg in cattle exhibited significant variation with age. However, pharmacokinetic/pharmacodynamic investigations in cattle of different ages are required to assess the impact of these pharmacokinetic alterations on clinical efficacy.

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