Disposition kinetics and dosage regimen of ceftriaxone in crossbred calves (short communication).

Disposition kinetics and urinary excretion of ceftriaxone were investigated in healthy crossbred calves after its single intravenous administration (10 mg kg-1). Based on kinetic parameters, an appropriate dosage regimen of ceftriaxone in calves was calculated. The peak plasma level of ceftriaxone at 1 min was 84.0 +/- 1.55 micrograms ml-1 which declined to 0.43 +/- 0.05 microgram ml-1 at 8 h. The value of elimination half-life (t1/2 beta), volume of distribution Vd (area) and total body clearance (ClB) were 4.39 +/- 0.63 h, 1.91 +/- 0.19 L kg-1 and 0.31 +/- 0.01 L kg-1 h-1, respectively. Approximately 41 per cent of total administered drug was recovered in the urine within 24 h of its administration. The plasma protein binding of ceftriaxone was found to be concentration dependent with an overall mean of 38.55 per cent. The binding capacity of ceftriaxone to plasma proteins and the dissociation rate constant of protein-drug complex were 20.1 x 10(-8) +/- 18.4 x 10(-8) mole g-1 and 1.07 x 10(-6) +/- 0.52 x 10(-6) mole, respectively. An appropriate intravenous dosage regimen of ceftriaxone in cattle would be 12 mg kg-1 repeated at 24 h.