The role of antibiotic pharmacokinetic studies performed post-licensing

Post-licensing pharmacometric studies can provide a better understanding of the pharmacokinetic (PK) alterations in special patient populations and may lead to better clinical outcomes. Some patient populations exhibit markedly different pathophysiology to general ward patients or healthy individuals. This may be developmental (paediatric patients), a manifestation of an underlying disease pathology (patients with obesity or haematological malignancies) or due to medical interventions (critically ill patients receiving extracorporeal therapies). This paper outlines the factors that affect the PK of special patient populations and describes some novel methods of antimicrobial administration that may increase antimicrobial concentrations at the site of infection and improve treatment of severe infection.

Comparative review of imipenem/cilastatin versus meropenem

INTRODUCTION

Carbapenems are broad-spectrum antibacterial molecules. Imipenem-cilastatin and meropenem are the two main molecules used in French healthcare services.

OBJECTIVE

We aimed to evaluate the relative strengths and weaknesses of these two molecules by considering their pharmacokinetic, pharmacodynamic, microbiological, and clinical properties. We demonstrated that imipenem-cilastatin and meropenem are not alike.

METHOD

Review of the literature by querying the MEDLINE network.

RESULTS

Imipenem-cilastatin is the first marketed molecule of the carbapenem class. It is more effective against Gram-positive cocci. Its stability does not allow for long infusions and its main adverse effect on the central nervous system limits its use. Meropenem is more effective against Gram-negative bacilli. Its stability and its milder adverse effects distinguish it from imipenem-cilastatin.

CONCLUSION

Meropenem is preferred for daily use in healthcare services when carbapenems are to be used.

Cerebrospinal pharmacokinetic and pharmacodynamic analysis of efficacy of meropenem in paediatric patients with bacterial meningitis

BACKGROUND

Meropenem is widely used for the treatment of paediatric patients with bacterial meningitis, but the pharmacodynamic (PD) basis for this has not been fully elucidated.

OBJECTIVES

A cerebrospinal pharmacokinetic (PK) and PD analysis was performed to identify the optimal dosage regimen for paediatric patients with inflamed central nervous system disease (bacterial men-ingitis).

PATIENTS AND METHODS

Paediatric data from three clinical studies were used to build a novel population PK model with a cerebrospinal fluid (CSF) compartment, assuming CSF clearance of 0.021 L/h from a physical-anatomical perspective. The bactericidal target attainment rates in CSF [50%T_>MIC(CSF)], after various dosage regimens, were simulated on the basis of reported or observed minimum inhibitory concentration (MIC) distributions and a newly developed population PK model including CSF concentrations. The effects of increased dose and/or prolonged infusion on target attainment were investigated.

RESULTS

Clinical data from 154 patients {mean age 30.6 [standard deviation (SD) 34.4] months, mean body weight 12.4 (SD 7.6) kg} were used for the population PK analysis. The flat profile of the CSF concentration-time curve and attainment of 50%T_>MIC(CSF) did not change markedly when the duration of infusion was increased, whereas attainment of 50%T_>MIC(CSF) was improved by increasing the dose from 20 to 40 mg/kg q8h for penicillin-resistant Streptococcus pneumoniae and Pseudomonas aeruginosa. Thirty-six patients who achieved satisfactory clinical cure showed at least 75.3%T_>MIC(CSF).

CONCLUSIONS

A high dose of meropenem (40 mg/kg q8h) is necessary to achieve clinical efficacy in paediatric patients with bacterial meningitis.

Pharmacokinetics-pharmacodynamics issues relevant for the clinical use of beta-lactam antibiotics in critically ill patients

Antimicrobials are among the most important and commonly prescribed drugs in the management of critically ill patients and beta-lactams are the most common antibiotic class used. Critically ill patient's pathophysiological factors lead to altered pharmacokinetics and pharmacodynamics of beta-lactams.A comprehensive bibliographic search in PubMed database of all English language articles published from January 2000 to December 2017 was performed, allowing the selection of articles addressing the pharmacokinetics or pharmacodynamics of beta-lactam antibiotics in critically ill patients.In critically ill patients, several factors may increase volume of distribution and enhance renal clearance, inducing high intra- and inter-patient variability in beta-lactam concentration and promoting the risk of antibiotic underdosing. The duration of infusion of beta-lactams has been shown to influence the fT > minimal inhibitory concentration and an improved beta-lactam pharmacodynamics profile may be obtained by longer exposure with more frequent dosing, extended infusions, or continuous infusions.The use of extracorporeal support techniques in the critically ill may further contribute to this problem and we recommend not reducing standard antibiotic dosage since no drug accumulation was found in the available literature and to maintain continuous or prolonged infusion, especially for the treatment of infections caused by multidrug-resistant bacteria.Prediction of outcome based on concentrations in plasma results in overestimation of antimicrobial activity at the site of infection, namely in cerebrospinal fluid and the lung. Therefore, although no studies have assessed clinical outcome, we recommend using higher than standard dosing, preferably with continuous or prolonged infusions, especially when treating less susceptible bacterial strains at these sites, as the pharmacodynamics profile may improve with no apparent increase in toxicity.A therapeutic drug monitoring-guided approach could be particularly useful in critically ill patients in whom achieving target concentrations is more difficult, such as obese patients, immunocompromised patients, those infected by highly resistant bacterial strains, patients with augmented renal clearance, and those undergoing extracorporeal support techniques.

Pharmacokinetic/Pharmacodynamic Analysis of Meropenem for the Treatment of Nosocomial Pneumonia in Intracerebral Hemorrhage Patients by Monte Carlo Simulation

BACKGROUND

Nosocomial pneumonia (NP) is a frequent complication among patients with intracerebral hemorrhage (ICH). However, there are currently no pharmacokinetic (PK) and pharmacodynamic (PD) data to guide meropenem dosing in these patients.

OBJECTIVE

To investigate the PK/PD properties of meropenem in these patients and whether the usual dosing regimens of meropenem (2-hour infusion, 1 g, every 8 hours) was suitable.

METHODS

A total of 11 patients with a diagnosis of ICH complicated with NP were selected in the emergency internal medicine and treated with a 1-g/2-hours extended infusion model. The plasma concentrations of meropenem were determined by high-performance liquid chromatography. PK parameters were estimated by plasma concentration versus time profile using WinNonlin software. The probability of target attainments (PTAs) of meropenem at different minimum inhibitory concentrations (MICs) based on percentage time that concentrations were above the minimum inhibitory concentration (%T>MIC) value were performed by Monte Carlo simulation.

RESULTS

The volume of distribution and total body clearance of meropenem were 55.55 L/kg and 22.89 L/h, respectively. Using 40%T>MIC, PTA was >90% at MICs ≤4 µg/mL. Using 80% or 100%T>MIC, PTA was >90% only at MICs ≤1 µg/mL.

CONCLUSIONS

The PK/PD profile of dosing regimens tested will assist in selecting the appropriate meropenem regimens for these patients. At a target of 40%T>MIC, the usual dosing regimens can provide good coverage for pathogens with MICs of ≤4 µg/mL. However, when a higher target (80% or 100%) is desired for difficult-to-treat infections, larger doses, prolonged infusions, shorter intervals, and/or combination therapy may be required.

Clinical pharmacokinetics of antibacterials in cerebrospinal fluid

In the past 20 years, an increased discrepancy between new available antibacterials and the emergence of multidrug-resistant strains has been observed. This condition concerns physicians involved in the treatment of central nervous system (CNS) infections, for which clinical and microbiological success depends on the rapid achievement of bactericidal concentrations. In order to accomplish this aim, the choice of drugs is based on their disposition toward the cerebrospinal fluid (CSF), which is influenced by the physicochemical characteristics of antibacterials. A reduced distribution into CSF has been documented for beta-lactams, especially cephalosporins and carbapenems, on the basis of their hydrophilic nature. However, they represent a cornerstone of the majority of combined therapeutic schemes for their ability to achieve bactericidal concentrations, especially in the presence of inflamed meninges. The good tolerability of beta-lactams makes possible high daily dose intensities, which may be associated with increased probability of cure. Furthermore, the adoption of continuous infusion seems to be a fruitful option. Fluoroquinolones, namely moxifloxacin, and antituberculosis drugs, together with the agents such as linezolid, reach the highest CSF/plasma concentration ratio, which is greater than 0.8, and for most of these drugs it is near 1. For all drugs that are currently used for the treatment of CNS infections, the evaluation of pharmacokinetic/pharmacodynamic parameters, on the basis of dosing regimens and their time-dependent or concentration-dependent pattern of bacterial killing, remains an important aspect of clinical investigation and medical practice.

Clinical pharmacokinetics of meropenem and biapenem in bile and dosing considerations for biliary tract infections based on site-specific pharmacodynamic target attainment

The present study investigated the pharmacokinetics of meropenem and biapenem in bile and estimated their pharmacodynamic target attainment at the site. Meropenem (0.5 g) or biapenem (0.3 g) was administered to surgery patients (n = 8 for each drug). Venous blood samples and hepatobiliary tract bile samples were obtained at the end of infusion (0.5 h) and for up to 5 h thereafter. Drug concentrations in plasma and bile were analyzed pharmacokinetically and used for a Monte Carlo simulation to predict the probability of attaining the pharmacodynamic target (40% of the time above the MIC). Both drugs penetrated similarly into bile, with mean bile/plasma ratios of 0.24 to 0.25 (maximum drug concentration) and 0.30 to 0.38 (area under the drug concentration-time curve). The usual regimens of meropenem (0.5 g every 8 h [q8h]) and biapenem (0.3 g q8h) (0.5-h infusions) achieved similar target attainment probabilities in bile (≥ 90%) against Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae isolates. However, against Pseudomonas aeruginosa isolates, meropenem at 1 g q8h and biapenem at 0.6 g q8h were required for values of 80.7% and 71.9%, respectively. The biliary pharmacodynamic-based breakpoint (the highest MIC at which the target attainment probability in bile was ≥ 90%) was 1 mg/liter for 0.5 g q8h and 2 mg/liter for 1 g q8h for meropenem and 0.5 mg/liter for 0.3 g q8h and 1 mg/liter for 0.6 g q8h for biapenem. These results help to define the clinical pharmacokinetics of the two carbapenems in bile while also helping to rationalize and optimize the dosing regimens for biliary tract infections based on site-specific pharmacodynamic target attainment.

Population pharmacokinetic analysis of meropenem in Japanese adult patients

WHAT IS KNOWN AND OBJECTIVE

Meropenem is frequently employed as an empirical treatment for serious infections, but there has been no report on its population pharmacokinetic parameters for Japanese patients. Our aim is to undertake a population pharmacokinetic analysis of meropenem using non-linear mixed effects model (NONMEM).

METHODS

Data from 68 patients were analysed via NONMEM with the first-order method. The participants' covariates, including gender, age, actual body weight, serum creatinine, serum albumin, serum total protein and creatinine clearance, were analyzed by the forward inclusion and backward elimination method to identify their potential influence on meropenem pharmacokinetics. The adequacy of the constructed model was assessed by goodness-of-fit plots and the precision of the parameter estimated at each step of the model development. To assess the robustness of the estimated parameter, bootstrap analysis was performed.

RESULTS AND DISCUSSION

The data were best described by a one-compartment model. The serum creatinine values modified by the below normal limit in our hospital (mSCR) were an influential covariate for clearance (CL): CL (L/h) = 11·1 × (mSCR/0·7)(-1). The volume of distribution was estimated as 33·6 L. The coefficient of variation of the inter-individual variability of CL and the residual variability were 52·1% and 0·827% μg/mL, respectively. A comparison of the population pharmacokinetic parameters of meropenem in the final model estimated in NONMEM with original data, and 1000 bootstrap samples shows that both sets of estimates were comparable, thereby indicating the robustness of the proposed model.

WHAT IS NEW AND CONCLUSION

A population pharmacokinetic model that satisfactorily described the disposition and variability of meropenem in our Japanese population is described. NONMEM analysis showed that the clearance of meropenem depended on modified serum creatinine. The results of this study should help Japanese patients on meropenem by improving the prediction accuracy of dosing using the Bayesian method.