Long-term elution of antibiotics from bone-cement: an in vivo study using the prosthesis of antibiotic-loaded acrylic cement (PROSTALAC) system.

A prospective study of 49 patients undergoing a modified 2-stage exchange arthroplasty for infected total hip and knee arthroplasties using the prosthesis of antibiotic-loaded acrylic cement (PROSTALAC) system with a variety of doses of tobramycin and vancomycin was performed. The intra-articular concentrations of tobramycin and vancomycin were measured at the time of removal of the PROSTALAC temporary spacer and reimplantation of a definitive joint arthroplasty prosthesis, at a mean 118 days following initial implantation. The 95% confidence interval of the intra-articular concentration of tobramycin (4.35-123.88 mg/L) was entirely above the breakpoint sensitivity limit for sensitive organisms when at least 3.6 g of tobramycin was used per package of bone-cement but was entirely below it when at most 2.4 g was used. Vancomycin elution was not as good; however, detectable levels were still present in most patients. There was a statistically significant increase in the elution of vancomycin when the dose of tobramycin was increased from at most 2.4 g to at least 3.6 g. The dose of vancomycin in the cement did not influence the elution of either tobramycin or vancomycin. On the basis of these results, the use of at least 3.6 g of tobramycin and 1 g of vancomycin per package of bone-cement is recommended when antibiotic-loaded cement spacers are used in 2-stage exchange arthroplasty for infected total hip and knee arthroplasties.