Reimplantation in infection. Elution of gentamicin from cement and beads

A prospective study was performed to evaluate the arthroplasty fluid, serum, and urine antibiotic levels in 38 patients implanted with gentamicin-impregnated cement and in 18 patients with gentamicin-impregnated beads. Radioimmune assays were performed on arthroplasty fluid, serum, and urine samples at various times after surgery. On day 1, high arthroplasty fluid levels of gentamicin were eluted from bead-implanted patients (mean, 36.9 micrograms/ml; range, 19.6-69.5) and cement-implanted patients (mean, 14.9 micrograms/ml; range, 2.7-38.9) with very low serum and urine levels. The arthroplasty levels of gentamicin obtained in bead-implanted patients on day 1 were 17 times higher, and in cement-implanted patients, seven times higher, than those obtained with intravenous administration of gentamicin. The serum and urine levels were approximately ten to 20 times less in patients with gentamicin-impregnated cement or beads compared to those levels obtained after intravenous administration. These very low systemic levels should preclude nephrotoxic and ototoxic effects. No toxic effects were observed in these patients. Bioactivity of gentamicin in the specimens was confirmed. Staphylococci were exquisitely sensitive, while Streptococci were moderately resistant to gentamicin. Both gentamicin-impregnated beads and cement appear safe and provide substantial local in vivo antibacterial activity.