Antibiotic prophylaxis for surgery in morbidly obese patients

The rate of wound infections in morbidly obese patients who underwent gastroplasty surgery at our institution was 16.5% compared with a rate of 2.5% in normal-weight patients who underwent clean-contaminated surgery. Both groups received 1 gm of cefazolin intramuscularly before surgery was performed. We hypothesized that this regimen of prophylaxis did not provide adequate tissue levels in the morbidly obese. Morbidly obese patients who were undergoing gastroplasty were randomly selected to receive 1 gm cefazolin in the buttock fat, buttock muscle, or by intravenous injection. A fourth group of morbidly obese patients received 2 gm of cefazolin intravenously. Normal-weight patients who were undergoing upper abdominal surgery received 1 gm of cefazolin intravenously. At incision and closure, both blood and tissue levels of cefazolin were significantly (p less than 0.001) lower for all morbidly obese patients who received 1 gm cefazolin when compared with the blood and tissue levels of the drug found in normal-weight patients. The cefazolin levels obtained were below the minimal inhibitory concentrations of greater than 2 micrograms/ml for gram-positive cocci and of greater than 4 micrograms/ml for gram-negative rods. Only when the morbidly obese patient received 2 gm cefazolin were both the serum and adipose tissue levels adequate. For a 4-month period, all morbidly obese patients received 2 gm cefazolin prophylaxis, and the wound infection rate dropped to 5.6% compared with the previous rate of 16.5% (p less than 0.03). We conclude that antibiotic prophylaxis must be specially tailored to the needs of these obese patients.