Pharmacokinetics and serum concentrations of cephapirin in neonatal foals.

This research paper explores how the body of a neonatal foal absorbs, distributes, metabolizes and eliminates the antibiotic cephapirin, and what the average concentration levels are in the blood after administration.

Study Overview

• The study was carried out on six healthy foals aged between 4 and 6 days. This aimed to demonstrate the pharmacokinetics of cephapirin in young horses, an age group in which bacterial infections can be prevalent and severe.
• A single intramuscular injection of sodium cephapirin, a cephalosporin type antibiotic, was given at a dosage of 20 mg/kg of body weight. The high dosage was likely chosen to ensure a measurable level of drug in the blood for the entire 8-hour monitoring period.

Measurements and Findings

• Following the injection, samples were taken at regular intervals over an 8 hour period to allow for the measurement of serum concentrations of cephapirin.
• The highest average concentration of cephapirin in the blood (21.2 micrograms/ml) was reached at approximately 10 minutes post-injection, representing the peak absorption of the drug.
• The study also reflected upon the elimination rate of cephapirin in the foal’s body. The calculated elimination rate constant was 1.06 per hour, and the half-life (the time taken for the concentration to reduce to half) was 0.70 hour. This shows the drug is rapidly absorbed and eliminated from the neonatal foal’s system which could affect how frequently the drug needs to be administered for effective treatment.

Distribution and Clearance

• The apparent volume of distribution at steady state was calculated to be 1.06 L/kg. This refers to the theoretical volume in which the total amount of drug would need to be uniformly distributed to produce the observed blood concentration. A high volume of distribution implies that the drug extensively distributes into the tissues of the body.
• The plasma clearance rate was established at 1,105 ml/hr/kg. Plasma clearance rate represents the volume of plasma from which the drug is completely removed per unit time. The high clearance rate, along with the short half-life, indicates that cephapirin is quickly cleared from the body of neonatal foals.