In vitro pharmacokinetics of antibiotic release from locally implantable materials

Local deposition of antibiotics has became increasingly popular in the management of open fractures or osteomyelitis, and several substances have been employed as the vehicle for delivery. Although the elution characteristics of some substances have been documented, a comparative study of the characteristics of the commonly used substances could establish the clinical indications for particular vehicles. Cylindrical pellets of uniform size (6 x 4 mm) were prepared from bone graft (BG), demineralized bone matrix (DBM), plaster of Paris (POP), or polymethylmethacrylate (PMMA), with 25 mg of tobramycin/g of substance in each pellet. The pellets were suspended in phosphate buffered saline, and the antibiotic concentration in the buffer was determined at various time intervals by an enzyme immunoassay. BG and DBM eluted 70 and 45% of their antibiotic load by 24 h, and negligible amounts were detected at 1 week; POP released 17% of its load by 24 h, with trace amounts detected at 3 weeks; and PMMA eluted 7% at 24 h, with trace amounts detected for as long as 14 days. These findings suggest that the optimal vehicle for local deposition of antibiotic depends on the clinical setting. BG and DBM may be best employed when brief antibiotic coverage is required (as for acute contaminated open fractures), whereas POP and PMMA may be better suited for long-term coverage (such as for established osteomyelitis).