Cefazolin antibacterial activity and concentrations in serum and the surgical wound in dogs.

An antibiotic selected for surgical antimicrobial prophylaxis must be present in the surgical site throughout the operation in concentration sufficient to prevent growth of contaminating pathogens. The antimicrobial spectrum, minimal toxicity, and low cost of cefazolin make this first-generation cephalosporin a logical choice for antimicrobial prophylaxis in small animal surgical procedures in which the normal microbiologic flora of skin and gastrointestinal tract are the most likely pathogens. Pharmacokinetic variables of cefazolin were determined in serum and surgical wounds in dogs. Drug concentration in interstitial fluid of muscle biopsy specimens taken at random from wound surfaces and in postoperative wound fluid samples were determined. Effective surgical wound concentration of cefazolin was defined as 4 micrograms/ml, a concentration that inhibited the growth in vitro of 100% of staphylococcal and 80% of Escherichia coli clinical isolates. After IV and SC administrations, cefazolin equilibrated rapidly between serum and the surgical wound, and concentrations in the 2 sites decreased in parallel. With a bolus dose of 20 mg/kg of body weight given IV at the beginning of surgery and repeated by SC administration at 6 hours, cefazolin concentration in the surgical wound remained > 4 micrograms/ml for longer than 12 hours.