http://repub.eur.nl/res/aut/5873/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/8663/ 1997-01-01T00:00:00Z We developed and applied pharmacokinetic-pharmacodynamic (PK-PD) models to characterize in vitro bacterial rate of killing as a function of ceftazidime concentrations over time. For PK-PD modeling, data obtained during continuous and intermittent infusion of ceftazidime in Pseudomonas aeruginosa killing experiments with an in vitro pharmacokinetic model were used. The basic PK-PD model was a maximum-effect model which described the number of viable bacteria (N) as a function of the growth rate (lambda) and killing rate (epsilon) according to the equation dN/dt = [lambda - epsilon x [Cgamma(EC50gamma + Cgamma)]] N, where gamma is the Hill factor, C is the concentration of antibiotic, and EC50 is the concentration of antibiotic at which 50% of the maximum effect is obtained. Next, four different models with increasing complexity were analyzed by using the EDSIM program (MediWare, Groningen, The Netherlands). These models incorporated either an adaptation rate factor and a maximum number of bacteria (Nmax) factor or combinations of the two parameters. In addition, a two-population model was evaluated. Model discrimination was by Akaike's information criterion. The experimental data were best described by the model which included an Nmax term and a rate term for adaptation for a period up to 36 h. The absolute values for maximal growth rate and killing rate in this model were different from those in the original experiment, but net growth rates were comparable. It is concluded that the derived models can describe bacterial growth and killing in the presence of antibiotic concentrations mimicking human pharmacokinetics. Application of these models will eventually provide us with parameters which can be used for further dosage optimization. http://repub.eur.nl/res/pub/8628/ 1996-01-01T00:00:00Z The most important pharmacodynamic parameter for beta-lactam antibiotics has been shown to be the time above the MIC, which is used as an argument to administer beta-lactam antibiotics by continuous infusion. Studies in vitro and in laboratory animals comparing efficacy of continuous and intermittent infusion of beta-lactam antibiotics generally show continuous infusion to be more efficacious. While comparative trials in humans are scarce and a significant difference was only found in subgroup analysis in one study, several case-reports support the use of continuous infusion. Arguments in favour and against continuous infusion are discussed. Although dose-ranging studies have not yet been performed in humans, the results from in-vitro and in-vivo experiments indicate that 4 x MIC for the infecting bacterium would be the target concentration. Pharmacokinetic studies which have been performed in humans during continuous infusion show that serum concentrations can be predicted from total clearance or, using population pharmacokinetic modelling, the elimination rate constant as obtained during intermittent infusion. A nomogram is presented which allows calculation of the daily dose to obtain the target steady state blood concentrations suggested by the susceptibility of the infecting bacterium, usually 4 x MIC. For bacteria with a low MIC, the daily dose may be substantially lower than that used in conventional dosing regimens, while in infections which are difficult to treat as a result of more resistant bacteria, continuous infusion may be more effective than an equivalent bolus dose.