Levofloxacin population pharmacokinetics and creation of a demographic model for prediction of individual drug clearance in patients with serious community-acquired infection - PubMed (original) (raw)

Levofloxacin population pharmacokinetics and creation of a demographic model for prediction of individual drug clearance in patients with serious community-acquired infection

S L Preston et al. Antimicrob Agents Chemother. 1998 May.

Abstract

Population pharmacokinetic modeling is a useful approach to obtaining estimates of both population and individual pharmacokinetic parameter values. The potential for relating pharmacokinetic parameters to pharmacodynamic outcome variables, such as efficacy and toxicity, exists. A logistic regression relationship between the probability of a successful clinical and microbiological outcome and the peak concentration-to-MIC ratio (and also the area under the plasma concentration-time curve [AUC]/MIC ratio) has previously been developed for levofloxacin; however, levofloxacin assays for determination of the concentration in plasma are not readily available. We attempted to derive and validate demographic variable models to allow prediction of the peak concentration in plasma and clearance (CL) from plasma for levofloxacin. Two hundred seventy-two patients received levofloxacin intravenously for the treatment of community-acquired infection of the respiratory tract, skin or soft tissue, or urinary tract, and concentrations in plasma, guided by optimal sampling theory, were obtained. Patient data were analyzed by the Non-Parametric Expectation Maximization approach. Maximum a posteriori probability Bayesian estimation was used to generate individual parameter values, including CL. Peak concentrations were simulated from these estimates. The first 172 patients were used to produce demographic models for the prediction of CL and the peak concentration. The remaining 100 patients served as the validation group for the model. A median bias and median precision were calculated. A two-compartment model was used for the population pharmacokinetic analysis. The mean CL and the mean volume of distribution of the central compartment (V1) were 9.27 liters/h and 0.836 liter/kg, respectively. The mean values for the intercompartmental rate constants, the rate constant from the central compartment to the peripheral compartment (Kcp) and the rate constant from the peripheral compartment to the central compartment (Kpc), were 0.487 and 0.647 h(-1), respectively. The mean peak concentration and the mean AUC values normalized to a dosage of 500 mg every 24 h were 8.67 microg/ml and 72.53 microg x h/ml, respectively. The variables included in the final model for the prediction of CL were creatinine clearance (CLCR), race, and age. The median bias and median precision were 0.5 and 18.3%, respectively. Peak concentrations were predicted by using the demographic model-predicted parameters of CL, V1, Kcp and Kpc, in the simulation. The median bias and the median precision were 3.3 and 21.8%, respectively. A population model of the disposition of levofloxacin has been developed. Population demographic models for the prediction of peak concentration and CL from plasma have also been successfully developed. However, the performance of the model for the prediction of peak concentration was likely insufficient to be of adequate clinical utility. The model for the prediction of CL was relatively robust, with acceptable bias and precision, and explained a reasonable amount of the variance in the CL of levofloxacin from plasma in the population (r2 = 0.396). Estimated CLCR, age, and race were the final model covariates, with CLCR explaining most of the population variance in the CL of levofloxacin from plasma. This model can potentially optimize the benefit derived from the pharmacodynamic relationships previously developed for levofloxacin.

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Figures

FIG. 1

FIG. 1

Probability distributions of pharmacokinetic parameters in the population. The marginal distributions, which indicate the probability of occurrence of pharmacokinetic parameter values in the population, are displayed. (A) Slope of _V_1 to body weight (VS; in liters/kilogram). (B) CL (in liters/hour). (C and D) _K_cp (KCP) and _K_pc (KPC), (in hours−1), respectively.

FIG. 2

FIG. 2

Three-dimensional probability distributions of pharmacokinetic parameters. (A to C) Three-dimensional probability distribution plots of the population for pharmacokinetic parameters. Parameters and units are as described in the legend to Fig. 1.

FIG. 3

FIG. 3

Observed versus MAP Bayesian-predicted concentrations in 272 patients. A scatter plot of observed versus MAP Bayesian-predicted concentrations based on pharmacokinetic parameter medians is shown. The slope and the intercept of the line are 1.01 and 0.0054, respectively. The slope is not significantly different from 1.0, and the intercept is not significantly different from 0.0. The _r_2 value is 0.966.

FIG. 4

FIG. 4

Measured versus predicted CL obtained with the demographic model. The measured versus predicted CL for the validation group (n = 100) obtained with the demographic model developed in this study is shown. Note that when the measured CL reaches approximately 13 liters/h, the predictive performance decreases (the model underpredicts CL).

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