Rifampin disposition in the horse: effects of age and method of oral administration.

This research investigates how the method and timing of administration affect oral absorption of rifampin in mature horses and 1-week old foals. The results show significant differences in how the drug is absorbed and processed, influencing its pharmacokinetic parameters.

Method and Timing of Rifampin Administration

• The study assessed the absorption of the antibiotic rifampin in five mature horses when administered in different ways and times.
• Methods included administering rifampin as a top dressing on grain or in corn syrup either 2 hours before or 2 hours after feeding.
• The researchers noted a significant delay in the time of maximum serum concentration when rifampin was given as a top dressing on grain, compared to when it was administered in corn syrup.
• They also observed an apparent, but insignificantly, lower oral absorption when the drug was given with grain.
• The study found no difference between administering the drug before or after feeding, but it was decided that giving rifampin 2 hours before feeding would be the chosen method for subsequent experiments.

Age Effects on Rifampin Disposition

• The next phase of the research involved examining how age impacted the disposition of rifampin.
• A new set of six, 1-week old foals were given rifampin (10 mg/kg) at increasing ages from 1 through 10 weeks using the chosen method of administration (2 hours prior to feeding).
• The study then measured and compared the pharmacokinetic disposition parameters at these different ages.
• The research found significant differences in the slope of the elimination phase (beta) and the area under the curve (AUC) at 1 week through 6 weeks versus 10 weeks.
• These metrics were also compared to the values in the mature horses from the first phase of the study, revealing significant differences.
• This suggests that age significantly influences how rifampin is absorbed and processed in horses.