Are Silver-Based Antimicrobial Catheters Falling Short of Expectations?

Silver-based antimicrobials may not be living up to their reputation when it comes to combating hospital-acquired infections (HAIs), Gertrude Gutierrez, a microbiologist at Innova Dynamics (San Francisco), speculated in a conference presentation at MD&M West this week. While silver-based antimicrobial technologies demonstrate promise for reducing instances of catheter-acquired urinary tract infections (CAUTIs), their efficacy remains questionable in the face of unimpressive study results and continued high rates of nosocomial infections, she says. If this is the case, what's next for antimicrobial technologies?

The associated high cost of care and high mortality rates, coupled with the fact that hospitals are no longer reimbursed for HAIs, has spurred development of technologies to address CAUTIs and other such common infections. Yet despite the rising prevalence of antimicrobial catheter use in clinical settings, mortality and infection rates remain unsettlingly high, according to Gutierrez. 

So, is silver not all it's cracked up to be? "Although silver catheters have so much data out there on them, efficacy appears to be mixed at this time," Gutierrez said. As evidence of her claim, she cited a 2006 study at Johns Hopkins in which approximately 1100 patients received silver-coated catheters and about 1900 patients were given a control, noncoated silicone catheter. Roughly 14% of the patients with antimicrobial-equipped catheters contracted a UTI; 16.5% of patients with the plain silicone catheter developed a UTI. This negligible discrepancy between a silver-based antimicrobial catheter and a control catheter, Gutierrez said, does not effectively demonstrate protection of patients.

But silver-coated catheters aren't the only antimicrobial catheters falling short of expectations, according to Gutierrez. She noted that nitrofurazone-impregnated catheters also showed little difference between UTI rates contracted while using an antimicrobial-impregnated catheter compared with a noncoated one. In contrast, minocycline-rifampin-impregnated catheters have shown the potential to be formidable opponents of UTIs, Gutierrez said. However, there is not currently enough data from which to draw firm conclusions.

In the hunt for new technologies to address the issue of CAUTIs and HAIs in general, researchers are exploring options such as encrustation and obstruction sensors as well as chemicals serving as biofilm inhibitors, Gutierrez said. In addition, her company, Innova Dynamics, has developed an antimicrobial technology that it claims has outperformed market-leading antimicrobial Foley catheters in studies.

"We have a surface technology that allows us to embed different antimicrobials onto the surface of various polymers," she explained. "This has proven to be a very effective and very durable fast-acting antimicrobial, antibiofilm, and antiinfection [technology]."

Rather than the common antimicrobial methods of a bulk incorporation or coating process, Innova Dyanmics' Innlay platform technology allows for antimicrobials to be embedded right at the surface of the polymer, facilitating surface exposure. In turn, this surface exposure affords a fast-acting antimicrobial performance, she said. In less than two hours, the Innlay-enhanced catheter was able to achieve log reduction far beyond that of the control silicone catheter in a study, she said.

While the Innlay platform technology sounds like a promising next-generation antimicrobial, more data are needed. That said, are the much-championed silver-based antimicrobial technologies in need of improvement? It sounds as though that's the case. Many existing antimicrobial technologies boast impressive results in their own studies, but it looks like perhaps we need more in vivo studies such as the Johns Hopkins one conducted in order to determine the true efficacy of current antimicrobial technologies on CAUTIs and other HAIs. --Shana Leonard