Pharmacokinetics of metronidazole and its concentration in body fluids and endometrial tissues of mares.

The article discusses a study on the pharmacokinetics of the drug metronidazole in healthy mares, its concentration in various body fluids, and tissues, and possible implications of the data for the treatment of bacterial pleuropneumonia.

Methodology and Findings

Six healthy adult mares were given an intravenous injection of metronidazole. Various data about the drug’s pharmacokinetics were collected, such as:

• The mean elimination rate was 0.23 per hour, and the mean elimination half-life was 3.1 hours.
• The apparent volume of distribution at steady state was 0.69 liters per kilogram, and the clearance was 168 milliliters per hour per kilogram.

A loading dose of the drug was given to each mare at time 0, followed by 4 maintenance doses by nasogastric tube. After this, concentrations of the drug were measured in different body fluids and tissues over time:

• The highest mean concentration in serum was about 13.9 micrograms per milliliter, recorded 40 minutes after the loading dose.
• Highest concentrations in the synovial and peritoneal fluid were 8.9 and 12.8 micrograms per milliliter respectively, recorded 2 hours after the loading dose.
• The lowest mean concentration in the urine was 32 micrograms per milliliter.
• The drug concentration in the cerebrospinal fluid (CSF) and the endometrial tissues was 4.3 micrograms per milliliter and 0.9 micrograms per gram respectively, recorded 3 hours after the fourth maintenance dose.

Implications for Treatment

Two sick mares with bacterial pleuropneumonia were given metronidazole along with other drugs including gentamicin, potassium penicillin, and flunixin meglumine IV. The pharmacokinetics of metronidazole and the serum concentrations in these mares were found to be similar to those in the healthy ones, indicating that the health status of the mares does not greatly affect the behavior of the drug in the mare’s body. This information would be useful for veterinarians while prescribing metronidazole for the treatment of infections in mares, regardless of their health status.