Cefazolin Dosing for Surgical Prophylaxis in Morbidly Obese Patients

Background: Cefazolin is used commonly to prevent surgical site infection (SSI) after operations on patients with morbid obesity (MO), but specific dosing guidelines are lacking. We hypothesized that cefazolin 2g given by intravenous (IV) push over 5min (IVP) or infusion over 30 min (INF) would suffice for 551 prophylaxis in MO (body mass index [BMI] 40-50 kg/m(2)), and cefazolin 3g would be sufficient in patients with super-morbid obesity (SMO) [BMI >50 kg/m(2)). Methods: Twenty-five patients undergoing elective surgical procedures were given a single dose of cefazolin: Ten with MO received 2g via.IVP (MO2-IVP), five with MO received 2g via 30-min infusion (MO2-INF), five with SMO received 2g via infusion (SMO2-iNF), and five with SMO received 3g via infusion (SMO3-INF). Serum cefazolin concentrations were measured 5, 30, 1.20, and 360 mm after initiation of the dose. The half-life of the drug was calculated for each patient, as was the time the concentration was above the minimum inhibitory free concentration (fT>MIC) using 8 mcg/mL as the breakpoint. The protective duration of each cefazolin dose was assessed using the pharmacodynamic target for /T.>MIC of 70%. Results: The mean cefazolin concentrations after 30 mm were similar in all groups; the mean concentrations at 120 and 360 min were 67.1-84.8 mcg/mL and 22.9-40.8 mcg/mL, respectively. The half-life ranged from 2.3 to 3.6h and was unaffected by administration method. The protective duration was 5.1h for MO2-IVP, 4.8h for MO2-INF, 5.8h for SMO2-INF, and 6.8h for SMO3-INF. Conclusions: A single 2-g dose of cefazolin appears to provide antibiotic exposures sufficient for most common general surgical procedures of <5-h duration, regardless of BMI.