Pharmacokinetics of cefuroxime in plasma and skin following IV-bolus administration in a rabbit model

The purpose of this thesis was (i) to select and validate an HPLC method for the determination of cefuroxime in microdialysis and plasma samples; (ii) to study the calibration of microdialysis probes by retrodialysis in vivo and in vitro; (iii) to determine the pharmacokinetics (PK) of cefuroxime in dermis (site of action) via microdialysis (MD) sampling; (iv) to study the pharmacokinetics of cefuroxime in plasma following IV-bolus administration.;Inadequate tissue penetration of antibiotics can lead to therapeutic failure and bacterial resistance. Pharmacokinetic evaluation of antibiotics should therefore be based on tissue rather than serum concentrations. Over several years, tissue concentration data obtained by methods such as tissue biopsies have flawed the correct interpretation of antibiotic tissue distribution. In most cases, only the concentration of free unbound antibiotic in the interstitial space fluid (ISF) at the infection site produces the antibacterial effect. Consequently, direct target site concentration measurements might be more relevant in predicting clinical response than the estimation of tissue concentration from those in the plasma. To monitor target site concentrations in animals and humans, several techniques (e.g. tissue biopsies, saliva and skin blister fluid sampling, imaging techniques, microdialysis) have been employed. In contrast to MD, which allows sequential sampling over time, traditional concentration measurements in bodily secretions or biopsy samples usually only yield a limited number of time points.;Microdialysis is a semi-invasive sampling technique. It has been employed for the in vivo measurement of antibiotic tissue pharmacokinetics. Owing to selective access to the target site for most anti-infective drugs, microdialysis satisfies regulatory requirements for pharmacokinetic distribution studies and has become a reference technique for tissue distribution studies.;The HPLC method selected and validated for the determination of cefuroxime in plasma and microdialysis samples consisted of a reversed phase C18 column, flow rate of 1 ml/min and a detection wavelength of 280 nm. Mobile phase used for microdialysis and plasma samples consisted of methanol: 0.1M phosphate buffer (pH 5) (1:3). The retention time was 5.35 min. The calibration curves for microdialysis samples were linear in the range of 50-10,000 ng/ml and 1-300 μg/ml with a correlation coefficient larger than 0.99. The lower limit of quantification (LLOQ) was 50 ng/ml and 1 μg/ml, for microdialysis and plasma samples respectively.;The kinetics of cefuroxime was investigated in 3 female pathogen-free New Zealand albino rabbits. Microdialysis probes were implanted into the skin of a tranquilized rabbit and perfused with lactated ringer's solution. Cefuroxime was administered as IV-bolus in a randomized cross-over experimental design in 3 separate doses of 25, 50, and 100 mg/kg. Blood and microdialysis samples were collected at selected time intervals. Retrodialysis was performed at the start of each experiment to assess probe recovery and correct the dialysate concentration to reflect the actual interstitial fluid concentration.;The results of these studies show that rabbit skin equilibrates with plasma in approximately 30 minutes and after that skin and plasma levels decline similarly. Because a 30 minute delay is usually not therapeutically relevant for cefuroxime, it can be concluded that plasma pharmacokinetics of cefuroxime can be correctly used to predict skin levels.