INDIVIDUALIZED AMOXICILLIN-CLAVULANATE DOSING RECOMMENDATIONS FOR CRITICALLY ILL CHILDREN WITH AUGMENTED CLEARANCE AFTER CARDIAC SURGERY.

Children who undergo cardiac surgery are prone to postoperative infections for which amoxicillin-clavulanate is a cornerstone antibiotic. Nevertheless, amoxicillin-clavulanate pharmacokinetics have not been studied in infants and children after cardiac surgery so far. Antibiotic exposure might be highly variable in this population due to the impact of growth, maturation and specific pathophysiological and surgery-induced alterations. The objective of this study was to develop evidence-based amoxicillin-clavulanate dosing recommendations, based on population pharmacokinetic analysis and probability of target attainment simulations in children after cardiac surgery. Critically ill children (aged 1 day to 15 years) who underwent cardiac surgery and who were treated postoperatively with amoxicillin-clavulanate (30 - 60 mg/kg/6h based on the amoxicillin component, infused in 30 min) were included. Up to five amoxicillin and clavulanate blood samples were collected per dose at predefined sampling times. Population PK analysis was performed using non-linear mixed-effects modeling software NONMEM. We collected 316 amoxicillin and 287 clavulanate blood samples from 37 patients. A three-compartment model for amoxicillin and a two-compartment model for clavulanate best described pharmacokinetics, with allometric weight scaling and maturation functions added a priori to scale for size and age. Clearance estimates were remarkably high, except in patients receiving vasopressors, which decreased clearance of amoxicillin-clavulanate by 1/3. Using a pharmacokinetic/pharmacodynamic target of 50%fT>MIC of 8 mg/L, patients not on vasopressors warrant 4-hourly dosing to achieve adequate drug exposure due to augmented amoxicillin clearance. Only in patients treated with vasopressors, the standard 6-hourly dosing regimen was sufficient to attain amoxicillin concentrations above the MIC for half of the dosing interval. Current amoxicillin-clavulanate dosing regimens for critically ill children after cardiac surgery need to be updated to avoid subtherapeutic concentrations and clinical failure due to augmented clearance. (ClinicalTrials.gov NCT02456974).

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