Regional Intraosseous Administration of Prophylactic Antibiotics is More Effective Than Systemic Administration in a Mouse Model of TKA

Background In human TKA studies, intraosseous regional administration (IORA) of prophylactic antibiotics achieves local tissue antibiotic concentrations 10 times greater than systemic administration. However, it is unclear if such high concentrations provide more effective prophylaxis. Questions/purposes We asked: (1) What prophylaxis dosage and route (intravenous [IV] versus IORA of prophylactic antibiotics) produce less in vivo bacterial burden compared with no-antibiotic controls? (2) Compared with controls, what prophylaxis dosage and route yield fewer colony-forming units (CFUs) in euthanized animals in a model of TKA? (3) Is prophylactic IORA of antibiotics more effective than same-dose IV antibiotic administration in reducing CFUs? Methods Mice (six to nine per group) were block randomized to one of six prophylaxis regimens: control, systemic cefazolin (C100 IV ), IORA of cefazolin (C100 IORA ), systemic vancomycin (V110 IV ), low-dose systemic vancomycin (V25 IV ), and low-dose IORA of vancomycin (V25 IORA ). Surgery involved placement of an intraarticular knee prosthesis, followed by an inoculum of bioluminescent Staphylococcus aureus strain Xen36. Biophotonic imaging assessed in vivo bacterial loads, and after 4 days bacterial load was quantified using culture-based techniques. Comparisons were made for each prophylactic regimen to controls and between same-dose IV and IORA of prophylactic antibiotic regimens. Results Mice treated with systemic high-dose vancomycin, IORA of vancomycin, or IORA of cefazolin had lower in vivo Staphylococcus aureus burdens (median area under curve, Control: 5.0 × 10 6 ; V110 IV : 1.5 × 10 6 , difference of medians 3.5 × 10 6 , p = 0.003; V25 IV : 1.94 × 10 6 , difference 3.07 × 10 6 , p = 0.49; V25 IORA : 1.51 × 10 6 , difference 3.5 × 10 6 , p = 0.0011; C100 IORA : 1.55 × 10 6 , difference 3.46 × 10 6 , p = 0.0016; C100 IV : 2.35 × 10 6 , difference 2.66 × 10 6 , p = 0.23.) Similar findings were seen with culture-based techniques on recovered implants. IORA of prophylactic antibiotics was more effective than same-dose IV administration in reducing bacterial load on recovered implants (median CFUs < 7.0 × 10 0 vs 2.83 × 10 2 , p = 0.0183). Conclusions IORA of prophylactic cefazolin and vancomycin was more effective than the same dose of antibiotic given systemically. The effectiveness of vancomycin in particular was enhanced by IORA of prophylactic antibiotics despite using a lower dose. Clinical relevance Our study