title: In vitro elution characteristics of vancomycin in a composite calcium phosphate/calcium sulfate bone substitute.
abstract: BACKGROUND
  Periprosthetic joint infection is a particularly difficult orthopedic problem, complicating a growing number of revision procedures. Joint debridement and systemic antibiotics are the mainstay of treatment, yet difficulty remains in maintaining a minimum inhibitory concentration of antibiotic at the localized site of infection.
  
  
  OBJECTIVE
  This study analyzes the elution characteristics of a 40%bwt calcium phosphate-60%bwt calcium sulfate composite, at varying concentrations of vancomycin.
  
  
  METHODS
  Four groups of varying concentrations of vancomycin (2.63%bwt, 5.13%, 9.76%, and 17.78%) were mixed with one pack of the composite cement. At designated time intervals up to 28 days, the antibiotic concentration was detected using fluorescence polarization immunoassay and the elution trends compared.
  
  
  RESULTS
  The elution rate of each of the four groups decreased over time. At almost all of the intervals, the elution rates of the higher concentration groups were significantly higher than the lower concentration groups (P < 0.05).
  
  
  CONCLUSIONS
  Calcium sulfate reabsorbs over a prolonged period, producing porosity which allows for new bone ingrowth through occupation of osteoprogenitor cells and osteoblasts; while calcium phosphate acts as a long-term osteoconductive matrix.
  
  
  CONCLUSIONS
  The results of this study suggest that vancomycin can be mixed affectively with a calcium sulfate/phosphate composite, both maintaining stability and eluting gradually over a clinically relevant period of time.
authors.affiliation: Hospital for Special Surgery, 535 East 70th St., New York, NY 10021 USA.
authors.forename: Xu
authors.initials: X
authors.lastname: Yang
authors.forename: Liza
authors.initials: L
authors.lastname: Osagie
authors.forename: Mathias P
authors.initials: MP
authors.lastname: Bostrom
keywords: antibiotic delivery; bone infection; drug delivery