Pharmacokinetics and Efficacy of Ceftriaxone in Staphylococcal Mastitis in Crossbred Cows Following Single Intravenous Administration

Background: Clinical mastitis is an important production disease of dairy animals, causing significant economic losses. Objective: Disposition kinetics of ceftriaxone was conducted in healthy lactating and staphylococcal mastitic crossbred cows in field condition following single-dose intravenous administration of only ceftriaxone. Methods: A single dose of ceftriaxone at 20 mg kg^-1 body weight was administered intravenously through jugular vein to six clinically healthy and six mastitic crossbred cows after proper diagnosis and three mastitic cows remained untreated (positive control). Blood and milk samples were collected at 0 (pre-dosing), 5, 15, 30 min, and 1, 24, 48, 72, 96 and 120 h post drug administration and analyzed for ceftriaxone and its active metabolite (ceftizoxime) by high-performance liquid chromatography. Results: Ceftriaxone achieved a peak mean plasma concentration of 131.67±1.83 μg mL^-1 at 5 min, which decreased sharply until 1 h (35.56±0.44 μg mL^-1) and was below detection limit at 24 h post drug administration in mastitic crossbred cows. On the other hand, ceftizoxime (active metabolite of ceftriaxone) achieved a peak level of 55.42±3.34 μg mL^-1 at 72 h and could not be detected at 120 h post drug administration in the milk of those mastitic crossbred cows. The Staphylococcus aureus colony count in mastitic crossbred cows was 49.33±6.55 × 10⁵ c.f.u./mL and the lowest colony count was achieved at 72 h with no colony at 120 h post drug administration. All the staphylococcal mastitis affected crossbred cows were cured on day 5. Conclusion: Ceftriaxone may prove to be effective in the treatment of staphylococcal mastitis in crossbred cows following single-dose intravenous administration at 20 mg kg^-1 body weight.