The pharmacokinetics of cefadroxil over a range of oral doses and animal ages in the foal.

This research analyzes the effect of age on the absorption, distribution, and elimination of the antibiotic cefadroxil in young foals. It was found that while the intravenous parameters did not significantly change with age, the oral bioavailability of the drug decreased as the foals aged.

Study Design

• The study involved five foals that were administered cefadroxil in a single intravenous dose (5 mg/kg) and a single oral dose (10 or 20 mg/kg) at varying ages – 0.5, 1, 2, 3 and 5 months.
• Various pharmacokinetic parameters such as terminal elimination rate constant (beta(po)), oral mean residence time (MRTpo), mean absorption time (MAT), rate constant for oral absorption (Ka), bioavailability (F), peak serum concentrations (Cmax), and time of peak concentration (tmax) were evaluated through a repeated measures analysis over the provided dose.

Results

• Across all observed animal ages, the parameters for the intravenous dose did not notably change over time.
• Upon oral administration, the study noted an increase in the speed of drug absorption with age. This was indicated by changes in parameters such as MRTpo, MAT, Ka, and tmax.
• However, oral bioavailability of cefadroxil experienced a significant decline as foals matured. A decline was observed from almost 100% at 0.5 months to around 14.5% when the foals were 5 months old.
• To evaluate the effect of the drug’s dose on the pharmacokinetic parameters, differing oral doses were administered to the foals at 1 month of age. Parameters such as beta(po) and F were found to be unaffected by the size of the dose.
• Cmax approximately doubled with each two-fold increase in dose.
• The study also found evidence of dose-dependent kinetics in parameters such as MRTpo, MAT, Ka, and tmax.

Implications

• The research results provide new insights into the pharmacokinetics of cefadroxil in young foals.
• This can assist in devising more effective drug administration strategies for sick foals, by carefully considering factors such as the age of the foal, the dose of the drug, and the method of drug administration.