Disposition kinetics of ceftriaxone and determination of its therapeutic dose in dogs

Purpose: To evaluate the disposition kinetics of ceftriaxone (CFZ) in dogs with a view to determining its therapeutic dose and dosing frequency. Methods: Twelve (12) Basenji dogs (n = 4), divided into 3 groups (A, B and C), were used for the study. Ceftriaxone was administered intramuscularly at doses of 12.5, 25, and 50 mg/kg once to groups A, B and C respectively. Plasma CFZ concentration was determined by agar well diffusion assay at 0.25, 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 h post-treatment, and the pharmacokinetic parameters were determined. Results: Intramuscular injection of CFZ to dogs resulted in rapid absorption, distribution and elimination (p < 0.05). The elimination half-life was short and did not change significantly with increase in dose. Serum concentration of CFZ changed significantly (p < 0.05) with increase in dose of CFZ. The maximum serum concentration (C-max, 15.00 +/- 1.18, 141.37 +/- 15.87 and 259 +/- 5.21 mu g/mL) for groups A, B and C respectively were significantly (p < 0.05) different. The steady state CFZ concentrations; 0.94, 8.81 and 16.19 mu g/mL for groups A, B and C, respectively, were significantly (p < 0.05) different. However, there was no significant difference in the time to reach steady state concentrations (T-max, 00 +/- 0.021, 4.00 +/- 0.10 and 4.30 +/- 0.12 for groups A, B and C respectively). The therapeutic dose of CFZ was therefore determined to be 25 - 50 mg/kg every 4 h. Conclusion: Ceftriaxone undergoes rapid elimination in dogs with a short elimination half-life, thus making it an inconvenient prescription for out-patients in veterinary clinics.