To determine the recommended concentrations of cefazolin to be used for antibiotic prophylaxis during paediatric cardiac surgery with extracorporeal circulation (ECC).

Twenty paediatric patients undergoing cardiac surgery with ECC and cefazolin antibiotic prophylaxis were included in the study. Blood samples for measurement of total cefazolin plasma concentration were collected at the following measurement time points: directly after skin incision, 15 min after ECC start, 5 min after ECC cessation and at skin closure. The target concentration was set for ≥40 mg/l, which corresponded to ≥8 mg/l of unbound cefazolin concentration.

The median total cefazolin plasma concentrations at the measurement time points were 62.8, 67.7, 45.8 and 34.2 mg/l, respectively, and target concentrations were achieved in 90%, 85%, 65% and 40% of children, respectively. Among patients who received ≥30 mg of cefazolin per 100 ml of ECC priming, target concentrations after ECC cessation were reached in 80% of patients, while in those with <30 mg cefazolin per 100 ml in 20% of patients (P = 0.031).

Direct extrapolation of antibiotic prophylaxis recommendations from adults to children may result in suboptimal antibiotic concentrations. An additional cefazolin dose to ECC priming appears necessary and the dosing should be based on ECC priming volume rather than on the weight of the patient.