Population pharmacokinetic and pharmacodynamic modeling of norvancomycin

Norvancomycin for the Treatment of Central Nervous System MRSA Infections: a Randomized Controlled Trial: Norvancomycin for the Treatment of Central nervous system MRSA infections

Combined intravenous and intrathecal administration of norvancomycin (NVCM) is routinely employed in treating methicillin-resistant Staphylococcus aureus (MRSA) ventriculitis in patients following craniotomy. However, the optimal dosing regimen, the pharmacokinetics (PK) of NVCM in cerebrospinal fluid (CSF), and the clinical outcome are yet to be elucidated. Herein, a single-center randomized controlled trial was conducted in the Neurosurgery Department of the Second Hospital of Hebei Medical University (Shijiazhuang, China). Patients with MRSA ventriculitis after craniotomy were randomly assigned to two groups. The control group received 800 mg NVCM intravenously every 12 h, and the experimental group received 800 mg NVCM intravenously every 12 h and 16 mg NVCM intrathecal administration every 24 h. The primary outcome was the length of therapy, while the secondary outcomes included the area under the concentration-time curve in 0-24 h/minimum inhibitory concentration ratio (AUC_0-24h/MIC) of NVCM in CSF. A total of 29 patients (14 in the experimental group and 15 in the control group) were included in this study. Of these, 24 constituted the final analysis population, with 12 in each group. The average length of therapy in the experimental group was markedly shorter than that of the control group (11.2 ± 2.6 days vs. 16.6 ± 5.2 days, P = 0.005), while the AUC_0-24h/MIC in the experimental group was significantly higher than that in the control group (2306.57 ± 928.58 vs. 46.83 ± 27.48, P <0.001) with no increase in adverse reactions. Combined intravenous and intrathecal administration can shorten the treatment time of intracranial infection without higher adverse reaction risks in our research. Further studies with larger sample size are warranted to verify its safety and efficacy.

Methodological features of clinical pharmacokinetic-pharmacodynamic studies of antibacterials and antifungals: a systematic review

BACKGROUND

Pharmacokinetic (PK)-pharmacodynamic (PD) indices relate measures of drug exposure to antibacterial effect. Clinical PK-PD studies aim to correlate PK-PD indices with outcomes in patients. Optimization of dosing based on pre-clinical studies means that PK-PD relationships are difficult to establish; therefore studies need to be designed and reported carefully to validate pre-clinical findings.

OBJECTIVES

To describe the methodological features of clinical antibacterial and antifungal PK-PD studies that reported the relationship between PK-PD indices and clinical or microbiological responses.

METHODS

Studies published between 1980 and 2015 were identified through systematic searches. Methodological features of eligible studies were extracted.

RESULTS

We identified 85 publications containing 97 PK-PD analyses. Most studies were small, with fewer than 100 patients. Around a quarter were performed on patients with infections due to a single specific pathogen. In approximately one-third of studies, patients received concurrent antibiotics/antifungals and in some other studies patients received other treatments that may confound the PK-PD-outcome relationship. Most studies measured antimicrobial concentrations in blood/serum and only four measured free concentrations. Most performed some form of regression, time-to-event analysis or used the Hill/Emax equation to examine the association between PK-PD index and outcome. Target values of PK-PD indices that predict outcomes were investigated in 52% of studies. Target identification was most commonly done using recursive partitioning or logistic regression.

CONCLUSIONS

Given the variability in conduct and reporting, we suggest that an agreed set of standards for the conduct and reporting of studies should be developed.

Population Pharmacokinetics and Pharmacodynamics of Norvancomycin in Children With Malignant Hematological Disease

Knowledge of pharmacokinetic (PK) behavior of norvancomycin (NVCM) in pediatric patients is lacking, which leads to empirical therapy in clinical practice. This study developed a population PK model of children aged 0-15 years; 112 opportunistic samples in total from 90 children were analyzed. The stability and prediction of the final model were evaluated by goodness-of-fit plots, nonparametric bootstrap, visual predictive check, and normalized prediction distribution errors. The PKs of NVCM in children was described by a 2-compartment model with first-order elimination along with body weight and estimated glomerular filtration rate as significant covariates on clearance. The population typical values of the PK parameters were as follows: clearance 0.12 L/kg/h, central compartment distribution volume 0.17 L/kg, peripheral compartment distribution volume 0.38 L/kg, and intercompartmental clearance 0.35 L/kg/h. Logistic analysis showed that the ratio of area under the concentration-time curve over 24 hours (AUC_0-24 ) to minimum inhibitory concentration (MIC) had the strongest correlation with clinical efficacy, and at least 80% clinical efficiency could be achieved when AUC_0-24 /MIC ≥ 221.06 was defined as the target. Monte Carlo simulation results suggested that a higher dose was required for this pediatric population in order to reach the target. The dosing regimen was optimized based on the final model. A population PK model of NVCM was first characterized in children with hematologic malignancy, and an evidence-based approach for NVCM dosage individualization was provided.

Factors Influencing Norvancomycin Concentration in Plasma and Cerebrospinal Fluid in Patients After Craniotomy and Dosing Guideline: A Population Approach

PURPOSE

Antibacterial spectrum and activity of norvancomycin are comparable with vancomycin, and it has been widely used in China. Norvancomycin can penetrate into the cerebrospinal fluid (CSF) through the damaged blood-brain barrier in patients after craniotomy. Because higher inter-individual variability was observed, we aimed to identify factors related to drug concentration to guide clinicians with norvancomycin dosing.

METHODS

After craniotomy, patients with an indwelling catheter in the operational area/ventricle were intravenously administered norvancomycin. Venous blood and CSF specimens were collected at a scheduled time for measuring drug concentrations. Blood and CSF data were fitted simultaneously with the use of the nonlinear fixed-effects modeling method to develop the population pharmacokinetic model. Covariate analysis was applied to select candidate factors associated with pharmacokinetic parameters. A model-based simulation was performed to find optimized regimens for different subgroups of patients.

FINDINGS

A 3-compartmental model (central, peripheral, and CSF compartments) with 2 elimination pathways (drug elimination from the kidney and CSF outflow) was developed to characterize the in vivo process of norvancomycin. The covariate analysis identified that weight and drainage amount were strongly associated with the central volume and the drug clearance from CSF, respectively. Goodness-of-fit and model validation suggested that the proposed model was acceptable. A dosage regimen table was created for specific patient populations with different weights and drainage amounts to facilitate clinical application.

IMPLICATIONS

We identified 2 clinical markers associated with plasma and CSF concentrations. The proposed simulation may be useful to clinicians for norvancomycin dosing in this specific population with normal kidney function.

Drug concentrations in the serum and cerebrospinal fluid of patients treated with norvancomycin after craniotomy

Intracranial infection by gram-positive cocci is commonly found after craniotomy. Norvancomycin was independently developed in China, and had demonstrated therapeutic capability against gram-positive infection. This study investigated the serum and cerebrospinal fluid (CSF) concentrations in patients that received intravenous injection of norvancomycin after craniotomy. Patients with an indwelling catheter in the operational area/ventricle after craniotomy were administered norvancomycin by two approaches: (1) The conventional group consisted of 14 cases that were infused with 0.8 g norvancomycin for 1 h, every 12 h; (2) The continuous administration group consisted of 14 cases that were infused with 0.8 g norvancomycin for 1 h, and then another 0.4 g for 11 h with extended infusion, followed by continuous infusion of 0.4 g norvancomycin for 12 h. Samples of serum and CSF were collected at different time-points to measure norvancomycin levels after administration. In the conventional and continuous administration groups, the peak serum concentrations of norvancomycin were 55.52 ± 26.04 and 59.22 ± 41.88 mg/L, respectively, while those at 24 h were 8.21 ± 6.04 and 8.01 ± 4.17 mg/L, respectively. Meanwhile, peak CSF concentrations were 16.31 ± 11.15 and 8.82 ± 8.91 mg/L, respectively, while those at 24 h were 6.12 ± 2.34 and 6.24 ± 4.38 mg/L, respectively. This preliminary study showed that for the early administration of standard doses of norvancomycin post-neurosurgery, the CSF concentration in both the conventional and continuous administration groups reached or exceeded the 90 % minimum inhibitory concentration (MIC₉₀, 2 mg/L) of target bacteria such as methicillin-resistant Staphylococcus aureus (MRSA).

Applications of pharmacometrics in the clinical development and pharmacotherapy of anti-infectives

With the increased emergence of anti-infective resistance in recent years, much focus has recently been drawn to the development of new anti-infectives and the optimization of treatment regimens and combination therapies for established antimicrobials. In this context, the field of pharmacometrics using quantitative numerical modeling and simulation techniques has in recent years emerged as an invaluable tool in the pharmaceutical industry, academia and regulatory agencies to facilitate the integration of preclinical and clinical development data and to provide a scientifically based framework for rational dosage regimen design and treatment optimization. This review highlights the usefulness of pharmacometric analyses in anti-infective drug development and applied pharmacotherapy with select examples.