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 2 g given by intravenous (IV) push over 5 min (IVP) or infusion over 30 min (INF) would suffice for SSI prophylaxis in MO (body mass index [BMI] 40-50 kg/m(2)), and cefazolin 3 g 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 2 g via IVP (MO2-IVP), five with MO received 2 g via 30-min infusion (MO2-INF), five with SMO received 2 g via infusion (SMO2-INF), and five with SMO received 3 g via infusion (SMO3-INF). Serum cefazolin concentrations were measured 5, 30, 120, and 360 min 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 fT>MIC of 70%. RESULTS: The mean cefazolin concentrations after 30 min 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 3.6 h and was unaffected by administration method. The protective duration was 5.1 h for MO2-IVP, 4.8 h for MO2-INF, 5.8 h for SMO2-INF, and 6.8 h 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.