Studies on the duration of antibiotic administration for surgical prophylaxis.

Patients undergoing 801 elective, clean-contaminated operations were assigned to one of the three following antibiotic regimens: 1) 1 g of cefazolin preoperatively, 2) 1 g of cefazolin preoperatively and another 1-g dose 3 hours later, and 3) 1 g of cefotetan preoperatively. These antibiotic regimens resulted in similar wound infection rates for procedures 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). Another 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 later if still in the operating room; 2) same as (1), plus 1-g doses every 8 hours for 24 hours. The longer period of antibiotic administration failed to improve the wound infection rate compared to the use of perioperative coverage only. These studies suggest that a single dose of preoperative antibiotic is sufficient for surgical prophylaxis when the operation is completed within 3 hours. Antibiotic coverage must extend 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 after the operation has been completed.