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.