Gentamicin serum concentrations in patients with gentamicin-PMMA beads for infected hip joints: a prospective observational cohort study.

BACKGROUND: Gentamicin-polymethylmethacrylate (PMMA) beads release gentamicin gradually, and high concentrations develop only locally. It is unclear how frequent and in which patients gentamicin serum concentrations are measurable and possibly lead to toxicity. The aim of this study was to investigate the measurability of gentamicin serum concentrations after the implantation of gentamicin-PMMA beads and to assess the nephrotoxicity of these beads. METHODS: In this observational cohort study, gentamicin and creatinine concentrations were measured in 34 serum samples of 23 patients with implanted gentamicin-PMMA beads for infected hip joints with our regular immunoassay (lower limit of quantitation 0.4 mg/L). Samples were also analyzed with an adjusted immunoassay with a lower limit of quantitation of 0.05 mg/L. RESULTS: Gentamicin serum concentrations were >0.4 mg/L in 9 of 34 (26%) of all the samples measured (both after the first implantation and change of beads) and in 5 of 23 patients (22%) after the first implantation of gentamicin-PMMA beads. Gentamicin serum concentrations were >0.05 mg/L in 31 samples (91%). Nephrotoxicity (defined as increase in serum creatinine >44 µmole/L and/or a relative increase >25%) occurred more frequently in patients with measurable gentamicin serum concentrations than in those without measurable gentamicin serum levels (57% versus 43%, P = 0.02). Both nephrotoxicity and gentamicin serum concentration could not be associated with the number of implanted gentamicin-PMMA beads. CONCLUSIONS: Gentamicin serum concentrations >0.4 mg/L can be measured after the implantation of gentamicin-PMMA beads in certain patients with infected hip joints. Furthermore, elevated (>0.4 mg/L) gentamicin serum concentrations are associated with nephrotoxicity in patients with gentamicin-PMMA beads for infected hip joints.