Pharmacokinetics and tissue fluid distribution of cephalexin in the horse after oral and i.v. administration.

The abstract summarizes a research study which aimed to understand how the drug cephalexin interacts within the bodies of adult horses, specifically studying how the drug moves and settles in the body after it is administered orally or through an injection (i.v.).

Objective of the Study

• The research was designed to determine the pharmacokinetics (the body’s effect on a drug), and tissue fluid distribution (where in body fluid the drug is distributed) of cephalexin in adult horses, after different methods of administration – oral and intravenous (i.v.).

Methodology

• A defined amount of cephalexin hydrate was administered to horses through injection, after which plasma samples were collected.
• Post this, a washout period was maintained, after which a different amount of cephalexin was administered orally. After this process, plasma, interstitial fluid (ISF) aqueous humor, and urine samples were collected.
• All collected samples were then analyzed through High-Pressure Liquid Chromatography (HPLC).

Findings

• The research found that after i.v. administration, the cephalexin had a half-life (time taken for the body to eliminate half of the drug) of 2.02 hours and a volume of distribution of 0.25 L/kg.
• Post oral administration, the maximum average concentration in plasma was found to be 3.47 microgram/mL with a half-life of 1.64 hours. The oral bioavailability (the extent and rate at which the drug enters the system) was roughly 5%.
• The ratio of Area Under the Curve (AUC) for interstitial fluid (ISF) to plasma was 80.55%, which corresponds to the percentage of the drug in the plasma that was not bound to protein (77.07%).
• Cephalexin was not detected in the aqueous humor (fluid in the eye), but was found concentrated in the urine, with an average concentration of 47.59 microgram/mL.
• No adverse events were observed during this study.

Conclusions and Further Research

• The study concluded that a dose of cephalexin, of 30 mg/kg given orally at 8-hour intervals can lead to plasma and interstitial fluid drug concentrations that are recommended for treating susceptible gram-positive bacteria in horses.
• However, due to the low oral bioavailability of cephalexin in horses, further research is needed to understand the effect of chronic dosing on the normal intestinal flora (the bacteria in the intestines).