Background: Cefazolin (CZL) is used commonly to prevent surgical site infection (SSI) after procedures on morbid obesity (MO) patients, but specific dosing guidelines are lacking. We hypothesized that CZL 2 g given either IV push (IVP) or over 30 min (INF) would suffice for SSI prophylaxis in MO, and CZL 3 g (C3G) would be sufficient in super-morbid obesity (SMO).

Methods: Fifteen MO patients (BMI 40-50 kg/m2) undergoing elective surgical procedures were studied. Ten received CZL 2 g via IVP, and five received CZL 2 g via INF. Five SMO patients (BMI > 50 kg/m2) received C3G over 30 min. Serum CZL concentrations were assayed at t=0, 30, 120, and 360 min using a validated high performance liquid chromatography method. The elimination rate constant was calculated using a linear regression of the terminal portion of the concentration versus time in minutes, and time above the minimum inhibitory concentration (TMIC) was calculated using a protein binding value of 85%

Results: Mean CZL concentrations (mcg/ml) after t=30 were similar in all groups (Figure). Administration method did not affect the elimination rate constant (IVP -0.024, 95% CI [-0.042 - -0.006], INF -0.033 [-0.042 - -0.024], C3G -0.028 [-0.054- -0.003]). For pathogens with MIC <8, TMIC was 3.75 hours for IVP, 3.42 hours for INF, and 4.87 hours for C3G.

Conclusions: Cefazolin is appropriate prophylaxis for MO patients against low-resistance pathogens. For hospitals with SSI pathogens with MIC < 8 mcg/ml, CZL 2 g can be administered by IVP or INF with redosing every 3-4 h. A 3 g dose of CZL may not be necessary for patients with SMO.