Disposition kinetics and bioavailability of piperacillin and cephapirin in mares.

The research paper focuses on examining the pharmacokinetics of antibiotics piperacillin and cephapirin in mares. It primarily investigates the disposition kinetics, absorption, and bioavailability of these antibiotics when administered through intravenous and intramuscular injections.

Understanding The Research

• The purpose of the study was to explore the pharmacokinetics, or how the body processes and eliminates the two antibiotics piperacillin and cephapirin when given to horses.
• A significant part of the study is determining the speed and extent at which the antibiotics are absorbed, distributed, metabolised, and eliminated from the body – this is generally referred to as disposition kinetics.
• The doses of the antibiotics given for the study were 430 mg/kg for piperacillin and 20 mg/kg for cephapirin using both intravenous and intramuscular methods.

Key Findings

• The paper highlights that the serum concentration to time curve of both antibiotics, after a single intravenous injection, followed a two-compartment open model, indicating pharmacokinetic behaviour where the drug moves between two different compartments in the body – central and peripheral.
• The transfer rates of the antibiotics between the compartments were quantified (from central to peripheral as k12 and peripheral to central as k21). The transfer rates of piperacillin were 0.46 h-1 (k12) and 0.56 h-1 (k21), while those for cephapirin were 0.52 h-1 (k12) and 0.49 h-1 (k21).
• The elimination half-life is the time it takes for the body to eliminate half of the drug from the system. Piperacillin and cephapirin were eliminated from the system with half-lives of 6.94 and 3.82 hours respectively, when administered intravenously.
• The total clearance (CItot.) rate indicates the efficacy of the mechanisms that eliminate the antibiotics from the body. The total clearance rates for piperacillin and cephapirin were 5.52 ml/min and 0.67 ml/min, respectively.
• After intramuscular injection, absorption half-lives [t0.5(ab)] were determined as 0.46 hours for piperacillin and 0.88 hours for cephapirin.
• The paper also mentioned maximum [Cmax.] and minimum [Cmin.] serum concentrations to establish a proper multiple dosage regimen – the higher concentration reach in the blood for both drugs and the minimum levels that need to be maintained for efficacy.
• The bioavailability numbers reported (85.47% for piperacillin and 67.89% for cephapirin) indicate the fraction of the administered drug that actually reaches systemic circulation and is available to exert its effect. These numbers are derived following intramuscular injection.
• The study concludes with in vitro protein bindings for both antibiotics, reporting 19.23% for piperacillin and 52.62% for cephapirin. Protein binding refers to the drug’s affinity to attach to proteins within the blood, which can impact the drug’s effectiveness.

Significance and Application

• This research is significant as it provides valuable insight into the behavioural kinetics of the antibiotics piperacillin and cephapirin in mares, which could lead to optimised dosage regimens to maximise therapeutic benefits while reducing the potential for adverse side effects.
• These findings can be used to inform veterinary practices and create standardised protocols for the use of these antibiotics in equine health care.