Pharmacokinetics and body fluid and endometrial concentrations of cephapirin in mares.

The research involves studying the pharmacokinetics of cephapirin, an antibiotic, in mares. It was administered intravenously and intramuscularly, and its concentration in body fluids and the endometrium were monitored over a specific time period.

Research Methodology

• The study involved six healthy adult mares that were each injected with a single dose of sodium cephapirin (20 mg/kg body weight) intravenously.
• The concentration of cephapirin in the serum was measured at regular intervals over a 6-hour period.
• Following this, each mare was given four intramuscular injections of sodium cephapirin at a dosage of 20 mg/kg.
• The concentrations of cephapirin in serum, synovial fluid, peritoneal fluid, cerebrospinal fluid (CSF), urine, and endometrium were measured at different time points.
• A parallel test was conducted using a less concentrated solution of cephapirin (250 mg/ml).

Key Findings

• The mean elimination rate constant was determined to be 0.78 hour-1 and the elimination half-life was found to be 0.92 hours.
• The apparent volume of distribution and drug clearance were estimated at 0.17 L/kg and 598 ml/hour/kg respectively.
• The maximum mean serum concentration observed was 14.8 micrograms/ml which occurred 25 minutes after the 4th injection.
• The highest mean concentrations in synovial and peritoneal fluids were 4.6 micrograms/ml and 5.0 micrograms/ml respectively, and they were observed 2 hours after the 4th injection.
• The highest mean concentration in the endometrium was 2.2 micrograms/g, which was observed 4 hours after the 4th injection.
• Significant amounts of the drug were excreted via urine with mean concentrations reaching up to 7,421 micrograms/ml.
• The drug was not found to readily penetrate the CSF.
• Following intramuscular administration of a less concentrated solution of the drug, the peak serum concentration was higher (25.0 micrograms/ml), but the total drug exposure over time (area under the serum concentration-time curve) was not significantly different.
• The drug had a bioavailability rate of 95% or more when administered intramuscularly.

The study provides valuable insights into how cephapirin is distributed, metabolized, and excreted in mares. These findings could be useful for dosage optimization in clinical veterinary medicine.