Study design: In vitro determination of minimum inhibitory concentrations (MICs) of gentamicin, cefazolin, and clindamycin, alone and in combination with iohexol against laboratory strains of Eschericia coli B, Staphylococcus aureus, and Staphylococcus epidermidis.
Objective: To study the effects of iohexol on the efficacy of gentamicin, cefazolin, and clindamycin.
Summary of background data: Prophylactic antibiotics have been advocated to prevent discitis following discography. Intravenous cefazolin administered before discography has been shown to penetrate the intervertebral disc. However, the use of systemic antibiotics for prophylaxis may lead to bacterial resistance. Intradiscal antibiotic administration is an attractive alternative to systemic antibiotic prophylaxis before discography, but there is no data documenting the efficacy of commonly used antibiotics in the presence of iohexol.
Methods: MICs were determined by adding standard concentrations of bacteria to serial dilutions of antibiotic with and without the addition of iohexol in Todd-Hewitt Broth medium. MICs were determined as the lowest concentration well that demonstrated inhibition of cell growth.
Results: Gentamicin, cefazolin, and clindamycin remain efficacious in the presence of iohexol. MICs were lower for cefazolin and gentamycin than for clindamycin. Iohexol alone also demonstrated some inhibition of cell growth.
Conclusion: This study supports the use of intradiscal antibiotics for prophylaxis of disc space infection during discography. lntradiscal placement of antibiotic should obviate the need for systemic antibiotic prophylaxis and its attendant risk of generating antimicrobial resistance.