Progress Not Panacea: Vancomycin Powder Efficacy and Dose Evaluated in an in-vivo Mouse Model of Spine Implant Infection

Abstract Background Intra-wound vancomycin powder (VP) has been rapidly adopted in spine surgery with apparent benefit demonstrated in limited, retrospective studies. Randomized trials, basic science, and dose response studies are scarce. Purpose This study aims to test the efficacy and dose effect of VP over an extended time course within a randomized, controlled in-vivo animal experiment. Study Design/Setting Randomized controlled experiment utilizing a mouse model of spine implant infection with treatment groups receiving vancomycin powder following bacterial inoculation. Methods Utilizing a mouse model of spine implant infection with bioluminescent Staphylococcus aureus, 24 mice were randomized into 3 groups: 10 infected mice with VP treatment (+VP), 10 infected mice without VP treatment (No-VP), and 4 sterile controls (SC). Four milligrams of VP (mouse equivalent of 1gram in a human) were administered prior to wound closure. Bioluminescence imaging was performed over 5 weeks to quantify bacterial burden. Electron microscopy (EM), bacterial colonization assays (Live/Dead) staining, and colony forming units (CFU) analyses were completed. A second dosing experiment was completed with 34 mice randomized into four groups: control, 2mg, 4mg, and 8mg groups. Results The (+VP) treatment group exhibited significantly lower bacterial loads compared to the control (No-VP) group, (p Conclusions Vancomycin powder provided an overall infection prevention benefit but failed to eradicate infection in all mice. Furthermore, the dose when halved also demonstrated an overall protective benefit, albeit at a lower rate. Clinical Significance Vancomycin powder is efficacious but should not be viewed as a panacea for peri-operative infection prevention. Dose alterations can be considered, especially in patients with kidney disease or at high risk for seroma.