Development and validation of a dosing nomogram for continuous infusion cloxacillin in infective endocarditis

Cloxacillin is the first-line treatment for methicillin-susceptible staphylococcal infective endocarditis (IE). The recommended dose is 12 g per day regardless of the patient characteristics, despite the importance of renal function on its pharmacokinetics.

We sought to build a population pharmacokinetics model of continuous infusion cloxacillin in IE patients to evaluate the influence of multiple covariates and then develop a nomogram based on significant covariates for individual adaptation.

We included patients of a local IE cohort who were treated with cloxacillin administered by continuous infusion, excluding those who received intermittent or continuous dialysis, extracorporeal membrane oxygenation or extracorporeal circulation. The population pharmacokinetic analysis was performed using Pmetrics. The influence of weight, ideal weight, height, body mass index, body surface area, glomerular filtration rate (GFR) calculated with the Chronic Kidney Disease Epidemiology Collaboration formula (both expressed in mL/min/1.73 m² and in mL/min) and serum protein level on cloxacillin pharmacokinetics was assessed. Accounting for relevant covariates, a dosing nomogram was developed to determine the optimal daily dose required to achieve a steady-state plasma concentration range of 20-50 mg/L with a probability ≥0.9.

A total of 114 patients (331 plasma concentrations) were included. A one-compartment model including GFR expressed in mL/min as a covariate was chosen. Using the nomogram, achieving the cloxacillin concentration target requires a daily dose ranging from 3.5 to 13.1 g for a GFR ranging from 20 to 125 mL/min.

This work provided a practical tool for cloxacillin dose adjustment in IE according to renal function.