Development and validation of a dosing nomogram for amoxicillin in infective endocarditis

Background Amoxicillin is the first-line treatment for streptococcal or enterococcal infective endocarditis (IE) with a dose regimen adapted to weight. Objectives Covariates influencing pharmacokinetics (PK) of amoxicillin were identified in order to develop a dosing nomogram based on identified covariates for individual adaptation. Patients and methods Patients treated with amoxicillin administered by continuous infusion for IE were included retrospectively. The population PK analysis was performed using the Pmetrics package for R (NPAG algorithm). Influence of weight, ideal weight, height, BMI, body surface area, glomerular filtration rate adapted to the body surface area and calculated by the CKD-EPI method (mL/min), additional ceftriaxone treatment and serum protein level on amoxicillin PK was tested. A nomogram was then developed to determine the daily dose needed to achieve a steady-state free plasma concentration above 4× MIC, 100% of the time, without exceeding a total plasma concentration of 80 mg/L. Results A total of 160 patients were included. Population PK analysis was performed on 540 amoxicillin plasma concentrations. A two-compartment model best described amoxicillin PK and the glomerular filtration rate covariate significantly improved the model when included in the calculation of the elimination constant Ke. Conclusions This work allowed the development of a dosing nomogram that can help to increase achievement of the PK/pharmacodynamic targets in IE treated with amoxicillin.