Characterisation of in vivo release of gentamicin from polymethyl methacrylate cement using a novel method

The purpose of this study was to investigate the in vivo elution kinetics of gentamicin from bone cement by assessing antibiotic levels in the urine.

Urinary samples of 35 patients who had undergone primary total hip arthroplasty were collected post-operatively. Gentamicin concentrations were analysed using the fluorescence polarisation immunoassay technique.

The mean duration of urinary gentamicin release in all cases was 43 days (range 13-95). There was still detectable gentamicin at the final collection in 20% (7/35) of cases, and in these cases, the mean gentamicin release was 71 days.

From the assessment of urinary gentamicin, we were able to demonstrate the biphasic gentamicin elution from bone cement. In addition, there were detectable concentrations of the antibiotic from the urinary samples for prolonged periods of up to two to six months. Our study indicates that the assessment of urinary antibiotics can offer a non-invasive method of monitoring the in vivo release kinetics of antibiotics from bone cement.