Antibiotic prophylaxis and tourniquet inflation in total knee arthroplasty

Twenty-four patients receiving total knee arthroplasty (TKA) were randomized into one of three groups based on tourniquet inflation one, two, or five minutes after administration 1 g cefazolin. Simultaneous serum, soft-tissue, and bone samples were obtained at regular intervals during surgery. All soft-tissue and bone samples were corrected for cefazolin content. The percentage of cefazolin penetration into soft tissue and bone was calculated using the area under the concentration time curve. Adequate cefazolin concentrations for soft tissue and bone were defined as greater than or equal to 4 x minimum inhibitory concentration90 (MIC90 = 1 microgram/ml) of cefazolin to Staphylococcus aureus and coagulase-negative staphylococci. Patients were similar in age, actual body weight, creatinine clearance, and length of tourniquet inflation. The median percentage of cefazolin penetration into soft tissue and bone for the five-, two-, and one-minute groups was 14.5% and 4.6%, 6.7% and 3.0%, and 5.9% and 4.6%, respectively; the percentage of penetration into soft tissue between the five- and one-minute groups was statistically significant. A higher percentage of patients achieved the desired cefazolin concentration (greater than or equal to 4 micrograms/g) if a five-minute interval was selected. The five-minute group achieved the highest mean ratios of concentration to MIC compared with the two- and one-minute groups, although the differences were not statistically significant. The standard 1 g of cefazolin with a five-minute interval between administration and tourniquet inflation resulted in adequate mean soft-tissue and bone concentrations for prophylaxis during TKA with a tourniquet time less than two hours. Additional doses are not warranted after tourniquet release.