Drug-eluting stents may help manage complications

Studies show a steady, predictable release of the incorporated drug over 120 days after implantation. Stents can either be coated with a drug or the agent can be built into the stent.

Dr. Denstedt's group currently is researching the effects of antibacterial triclosan-loaded ureteral stents, which are commercially available in Canada and Europe. In an initial trial in a rabbit model infected with bacteria, the stents had "significantly decreased colony counts and, in a number of instances, eradicated the infection," he reported.

"Encrustation is one of the major unsolved problems [of stents] in urology. It hasn't changed one iota since the Egyptians were putting in papyrus catheters," Dr. Denstedt said. "Most stents or catheters will encrust within a 3-month time frame."

Fifty percent of patients undergoing long-term catheterization experience recurrent encrustation and blockage. In one study, 90% of retrieved stents were encrusted with adherent pathogens. Catheters need to be changed every 6 weeks, and antibiotics are needed to prevent bacterial infection, Dr. Denstedt said.

Creating the perfect stent

The ideal stent would be biocompatible, radiopaque, rigid, comfortable for patients, and resistant to infection and encrustation. However, no stent is yet available that meets these criteria. Synthetic polymer compounds, particularly silicone, are currently the most useful biomaterials for both catheters and stents, Dr. Denstedt said.

"We are on the cusp of changes with new materials. If a Foley catheter were invented that could stay in for 1 year, and the same for stents, it would have a major impact in our specialty, and it would include some substantial economic benefits," he said.

Development of an indwelling urethral catheter that resists encrustation for 6 months, an internal ureteral stent that can resist encrustation up to a year, or a suprapubic valve catheter that could stay in place for 2 years would be substantial improvements, he pointed out.

He suggested that encrustation-resistant stents would also benefit high-risk patients, including those who are pregnant, who have metabolic stone disease, or who are susceptible to urinary tract infections, such as patients undergoing transplant and those with neurogenic bladder.

Stent-related pain remains a significant problem, and drug-eluting stents may play a role in pain management as well.

"When you put a stent in a patient, they are plagued by dysuria. The intuitive thing is build a drug into a stent to provide a pain-free stent," he said.

Most of the morbidity associated with ureteroscopy arises from stent-related problems following the procedure, Dr. Denstedt said. As a result, he and colleagues have conducted research aimed at eliminating stent use altogether in certain ureteroscopy patients.

In their initial study of 58 patients who underwent uncomplicated ureteroscopic intracorporeal lithotripsy, pain symptoms were significantly greater in stented patients (p<.005). When the stent was removed, no difference in pain symptoms at follow-up was seen between stented and unstented patients. The University of Western Ontario now leaves stents in only about 60% of ureteroscopy patients, he said.

Dr. Denstedt is a consultant to Boston Scientific.