STUDIES ON THE DURATION OF ANTIBIOTIC ADMINISTRATION FOR SURGICAL PROPHYLAXIS

Patients undergoing 801 elective, clean-contaminated operations Were a ssigned to one of the three following antibiotic regimens: 1) 1 g of c efazolin preoperatively, 2) 1 g of cefazolin preoperatively and anothe r 1-g dose 3 hours later, and 3) 1 g of cefotetan preoperatively. Thes e antibiotic regimens resulted in similar wound infection rates for pr ocedures completed within 3 hours. When the procedure lasted more than 3 hours, the 6.1 per cent infection rate noted when a single dose of cefazolin was given proved significantly greater than the 1.3 per cent infection rates associated with the use of two doses of cefazolin or a single dose of the longer acting antibiotic, cefotetan (P < 0.01). A nother series of 768 patients undergoing biliary and gastrointestinal tract operations were assigned to one of two antibiotic regimens: 1) a preoperative dose of 1 g of cefazolin and another 1-g dose 3 hours la ter if still in the operating room; 2) same as (1), plus 1-g doses eve ry 8 hours for 24 hours. The longer period of antibiotic administratio n failed to improve the wound infection rate compared to the use of pe rioperative coverage only. These studies suggest that a single dose of preoperative antibiotic is sufficient for surgical prophylaxis when t he operation is completed within 3 hours. Antibiotic coverage must ext end for the duration of longer operations. A second dose of antibiotic or a single preoperative dose of an extended half-life antibiotic are equally effective. There is no value to administering antibiotics aft er the operation has been completed.