Pharmacokinetics of ciprofloxacin in calves following a single intramuscular and subcutaneous administration

The present study was undertaken in calves to determine the pharmacokinetic behaviour of ciprofloxacin following a single intramuscular and subcutaneous administration @ 5 mg/kg. Blood samples were collected at different time intervals, and ciprofloxacin concentrations were determined using spectrofluorometric assay method and the pharmacokinetic determinants were calculated using one compartment open model. Appreciable plasma concentrations of ciprofloxacin could be detected in plasma within 0.16 h of drug administration by either of the routes and the peak plasma levels of 1.16±0.16 and 0.88±0.15μg/ml were observed at 1.0 and 0.5 h, respectively, after IM and SC administration. The levels gradually declined to 0.32±0.04 and 0.34±0.07 μg/ml at 6 and 3 h, respectively. The respective absorption and elimination half life values were 0.27 and 3.43 h after IM and 0.15 and 1.89 h after SC administration. Vdarea values of more than 1 litre/kg in calves in the present study suggested that ciprofloxacin has excellent ability to penetrate into body fluids and tissues. In view of the concentration-dependent killing effect and post-antibiotic effect of ciprofloxacin, it may not be unreasonable to suggest its administration once a day at 24 h interval. However, pharmacokinetic/pharmacodynamic relationship parameters values in calves did not suffice its administration at 5 mg/ kg body weight as the desired Cmax/MIC value of >8–12 and AUC/MIC value of >100 were not achieved. Therefore, ciprofloxacin may be administered to calves at higher dose rates i.e. at 10 mg/kg and/or repeated at 12 h interval, in more severe bacterial infections if the MIC values against the susceptible microbes are more than >0.25 μg/m