Conditioning film deposition on ureteral stents after implantation

Three types of ureteral stents were used in a study of 53 patients. Following extracorporeal shock wave lithotripsy, the stents were implanted and retained for periods of between 3 and 40 days. Each patient received daily antibiotic therapy with either ciprofloxacin or trimethoprim. After removal, the devices were analyzed for adherent bacteria and encrustations. The study showed that a conditioning film became deposited onto the stents upon implantation, changing the surface characteristics of the biomaterials. Dense encrustations were found to be least on a low surface energy device. No differences were found related to patient age and gender or duration of stent insertion. Flakiness and apparent sloughing of the stent surfaces was observed in some devices, raising concerns as to what actually happens to medical devices when exposed to the host urinary tract. Bacteria were recovered from the urine of three patients and the stents of four patients treated with trimethoprim. Five stents had bacterial biofilms detected by SEM. The actual clinical end-point was not the focus of this study, but no patients became septic. Our goal was to demonstrate conclusively in humans that medical devices do develop conditioning films upon implantation, and that they can be susceptible to bacterial colonization even during antibiotic treatments. The kidneys of stented patients are clearly at risk of infection, and only by proper selection of a stent type and appropriate antibiotic coverage can this risk be significantly reduced.