Effect of Body Weight on Cefazolin and Vancomycin Trabecular Bone Concentrations in Patients Undergoing Total Joint Arthroplasty.

BACKGROUND

Effective use of prophylactic antibiotics decreases the incidence of surgical site infections (SSIs) after total joint arthroplasty (TJA). The purpose of this prospective study was to determine the viability of weight-based dosing protocols for cefazolin and vancomycin to determine if appropriate minimum inhibitory concentrations (MIC) are met.

METHODS

Trabecular bone was harvested from discarded bone samples from 34 patients undergoing total knee arthroplasty (TKA) and total hip arthroplasty (THA). The cefazolin and vancomycin concentrations were determined in the trabecular bone using high-performance liquid chromatography.

RESULTS

No difference was noted in bone concentration with respect to patient weight for cefazolin. Regarding vancomycin, a substantial difference was noted in trabecular bone concentrations with respect to patient weight with lower body mass index (BMI) achieving greater concentrations. Using the current weight-based protocol of antibiotic prophylaxis, 84% and 87% of patients receiving vancomycin and cefazolin, respectively, achieved bone concentrations above the MIC.

CONCLUSIONS

Our assessment of trabecular concentration of cefazolin during TJA did not show any differences with respect to patient weight. However, vancomycin concentrations did show a difference with respect to BMI but this may be the result of the specific weight-based dosing protocol of vancomycin. Whereas the majority of cases were able to achieve adequate antibiotic concentrations in bone, further studies may be required to determine if increasing the pre-operative dosage of antibiotics is mandated given the findings of this pilot study.