Perioperative antibiotic prophylaxis in the gastric bypass patient: Do we achieve therapeutic levels?

Background. Perioperative surgical antibiotic prophylaxis requires that therapeutically effective drug concentrations be present in the tissues. Methods. Patients undergoing Roux-en-Y gastric bypass for morbid obesity were given 2 g cefazolin preoperatively, followed by a second dose at 3 hours. Thirty-eight patients were each assigned to 1 of 3 body mass index (BMI) groups: (A) BMI = 40-49 (N = 17); (B) BMI = 50-59 (N = 11); (C) BMI greater than or equal to 60 (N = 10). Multiple timed serum (baseline; incision, 15, 30, 60 minutes; prior to second prophylactic dose; and closure) and tissue (skin, subcutaneous fat, and omentum) specimens were collected and cefazolin concentration analyzed by microbiological assay. Results. No significant difference was observed in intraoperative fluid replacement or blood loss among BMI groups. Serum antimicrobial concentrations exceeded resistance breakpoint (32 mul/mL) in 73%, 68%, and 52% of BAH groups A, B, and C, respectively. No significant difference in cefazolin concentration was observed in mean incisional skin and closure tissue specimens in groups A, B, and C. A significant decrease in cefazolin concentration was noted in closure adipose (P = .04), initial (p = .03) and closure omentum (p = .05) tissues in groups B and C compared with A. Over 90% of serum samples exhibited therapeutic concentrations covering 53.8% of gram-positive and 78.6% of gram-negative surgical pathogens. However, therapeutic tissue levels were achieved in only 48.1%, 28.6%, and 10.2% of groups A, B, and C, respectively. Conclusions. Pharmacokinetic analysis suggests that present dosing strategies may fail to provide adequate perioperative prophylaxis in gastric bypass patients.