Amikacin sulfate in mares: pharmacokinetics and body fluid and endometrial concentrations after repeated intramuscular administration.

This study aimed to understand the effects of repeated intramuscular administration of amikacin sulfate in mares, particularly focusing on its concentrations in different body fluids and the endometrium. The study did not find significant differences in elimination rate and volume of distribution between the first and fifth injections.

Study Design: Administration of Amikacin Sulfate

• Six mares were involved in the study, given five intramuscular injections of amikacin sulfate with 12-hour intervals between doses.
• The dosage used was 7 mg/kg of body weight.
• The study also analyzed one mare with septic meningitis, especially comparing the amikacin concentrations in cerebrospinal fluid (CSF) with those in healthy mares.

Measurement of Amikacin Concentrations

• Researchers measured serum amikacin concentrations at specific intervals throughout the study.
• The concentration of amikacin in synovial, peritoneal, endometrial, and urine were determined after the last injection.
• For three out of six mares, the concentration of amikacin was measured in the CSF at regular intervals.

Results: Amikacin Concentrations

• The mean serum amikacin concentrations peaked 1 to 2 hours after intramuscular injection.
• Following the fifth injection, the highest mean serum concentration recorded was 19.2 micrograms/ml (1.5 hours after administration).
• The highest mean synovial concentration was 10.8 micrograms/ml (2 hours after the fifth injection), while the highest mean peritoneal concentration was 16.2 micrograms/ml (3 hours after the fifth injection).
• The mean endometrial amikacin concentration was 2.5 micrograms/g (1.5 hours after the fifth injection).
• In the mare with meningitis, amikacin reached a CSF concentration of 0.97 micrograms/ml, whereas amikacin wasn’t detected in the CSF of healthy mares.
• The urine concentrations of amikacin reached a peak at 1,458 micrograms/ml.

Pharmacokinetic Values

• The elimination rate constant was estimated at 0.31/hour after the first injection and 0.28/hour after the fifth injection.
• The drug’s half-life was calculated at 2.3 hours for the first injection and 2.6 hours for the fifth injection.
• The apparent volume of distribution was estimated at 0.26 L/kg after the first injection and 0.30 L/kg after the fifth injection.
• The researchers did not observe significant differences in the elimination rate constant or apparent volume of distribution between the first and fifth injections.