Comparative pharmacokinetics of minocycline in foals and adult horses.

The study presents a comparison of how the antibiotic minocycline behaves in the body (its pharmacokinetics) of foals and adult horses, finding a higher absorption of the drug in foals compared to adults when given orally. Also, it suggests a dosage that could be beneficial for treating bacterial infections in foals.

Design and Methodology

• This study involved six healthy 6- to 9-week-old foals and six adult horses. Minocycline, an antibiotic, was given to these participants.
• The antibiotic was administered intragastrically (IG or into the stomach) and intravenously (i.v. or into the vein).
• The dosage for intragastric administration was 4 mg/kg, and for intravenous, it was 2 mg/kg.
• For foals, five additional oral doses were administered at 12-hour intervals, which was not specified for adult horses.
• The researchers then measured the concentration of minocycline in various body fluids such as plasma, urine, synovial fluid, and cerebrospinal fluid (CSF) using a microbiological assay.
• Minocycline concentrations in pulmonary epithelial lining fluid (PELF) and bronchoalveolar (BAL) cells were measured using liquid chromatography-tandem mass spectrometry.

Results

• The elimination half-life of minocycline in foals, after i.v. administration, was 8.5 ± 2.1 hours. The systemic clearance was 113.3 ± 26.1 mL/h/kg and the apparent volume of distribution was 1.24 ± 0.19 L/kg.
• The same variables, when determined in adult horses, were not significantly different from those in foals.
• The bioavailability of minocycline, which refers to the percentage of the drug that enters the circulation and can have an active effect, was significantly higher in foals (57.8 ± 19.3%) than in adult horses (32.0 ± 18.0%). This indicates that the drug is absorbed more effectively in foals when administered orally.
• The concentration of minocycline in PELF was higher than in other body fluids. This could indicate the drug’s significant presence in the respiratory tract, potentially making it effective for respiratory infections.
• The study concludes that an oral dosage of minocycline at 4 mg/kg every 12 hours might be suitable for treating susceptible bacterial infections in foals.