Pharmacokinetics of ceftriaxone in healthy horses

Five healthy Equidae (4 horses and one pony) were given a single i.v. dose of ceftriaxone (50 mg/kg bwt) to determine the pharmacokinetics and concentration in cerebrospinal fluid (CSF). Blood was drawn from an i.v. jugular catheter and CSF from a pre-placed, intrathecal catheter. Serum and CSF concentrations were determined by high performance liquid chromatography. The mean serum concentration of ceftriaxone was 144.7 micrograms/ml 15 min after injection and declined to 0.3 microgram/ml 10 h after injection. The elimination rate constant (lambda 2) was 0.63 +/- s.e. 0.23/h, the elimination half-life (t 1/2) was 1.62 +/- s.e. 0.42 h and the apparent volume of distribution at steady state (Vd(ss)) was 330.8 +/- 11.8 ml/kg bwt. Clearance was 312.7 +/- 38 ml/h/kg bwt and mean residence time was 1.13 +/- 0.14 h. Mean CSF concentration was 0.60 +/- 0.14 microgram/ml at 3 h after injection and 0.4 +/- 0.31 microgram/ml at 8 h. Ceftriaxone may be useful in the treatment of bacterial infections in horses. Its ability to penetrate the CSF should make it effective in the treatment of bacterial meningitis.