Liquid Gentamicin in Bone Cement Spacers: In Vivo Antibiotic Release and Systemic Safety in Two-Stage Revision of Infected Hip Arthroplasty

Background: Powdered antibiotics are widely used in acrylic bone cement. Liquid antibiotics, however, have rarely been employed. This study investigated the application of liquid gentamicin, a much less costly antibiotic with a broad antimicrobial spectrum, in bone cement to treat musculoskeletal infections. Methods: Forty-two patients undergoing two-stage revision hip arthroplasty for periprosthetic infection were managed with an interim cement spacer loaded with liquid gentamicin (480 mg per 20 mL pack of cement monomer) with or without vancomycin (3.0 g per 40 g pack cement polymer). Serum and aliquots of drain-age collected after the first-stage surgery; joint fluid obtained at the time of the second-stage surgery were analyzed for antibiotic concentrations and bioactivity. Antibiotic levels in the peripheral blood and renal function were also monitored. Results: Antibiotic levels in joint fluid peaked on the first day after implantation of the spacer and then gradually declined during the first week, with levels of gentamicin and vancomycin reached 43.6 mg/L +/- 12.3 mg/L and 485.5 mg/L +/- 103.5 mg/L, respectively. Bioassay confirmed the antimicrobial activity of the released antibiotics. The systemic antibiotic concentrations were below detectable levels in the majority of patients, and no nephrotoxicity was noted. At a mean 87 days after implantation, antibiotic concentrations in joint fluid remained clinically effective (gentamicin, 5.1 mg/L +/- 2.2 mg/L and vancomycin, 21.6 mg/L +/- 8.5 mg/L). Conclusions: Incorporation of liquid gentamicin in bone cement spacers led to effective drug delivery with systemic safety. Substantial health care dollars could be saved by the use of liquid gentamicin in bone cement to treat musculoskeletal infections.