Pharmacokinetics and concentrations of ceftiofur sodium in body fluids and endometrium after repeated intramuscular injections in mares.

Each of 5 healthy mares was given 5 consecutive IM injections of ceftiofur sodium (2 mg/kg of body weight; 50 mg/ml) at 12-hour intervals. Ceftiofur concentrations were measured serially in serum, synovial fluid, peritoneal fluid, and urine, and were measured in CSF and endometrial tissue after the fifth dose. Mean elimination rate constant was 0.354 +/- 0.101 h-1 and elimination half-life was 2.49 +/- 0.49 hour. Mean serum ceftiofur concentrations peaked approximately 1 hour after each injection. The highest mean ceftiofur concentration was 5.09 micrograms/ml at 1 hour after the fifth dose for serum, 3.02 micrograms/ml at 2 hours after the fifth dose for synovial fluid, and 3.23 micrograms/ml at 4 hours after the fifth dose for peritoneal fluid. Mean urine concentrations reached 15.72 micrograms/ml at 1 hour after the fifth dose. Ceftiofur was not detected in CSF or endometrial tissue. None of the mares had adverse reactions to the drug.