Inflatable penile prosthesis coatings show minimal effect on bacterial growth

December 1, 2009

Infection-retardant coatings on penile prostheses, which have been shown to reduce primary implantation infection rates by more than half, appear to have minimal effect on bacterial growth based on culture data as found at the time of revision surgery.

However, a thorough washout during revision surgery may be sufficient to engender a significant reduction in overt clinical infection rates, researchers found.

The findings were presented in a study of bacterial infection (biofilm) on prostheses coated with antibacterial compounds as compared to bacteria on uncoated prostheses. The difference in infection rates between the two prostheses seemed surprisingly small. The researchers, led by Gerard Henry, MD, a urologist with Regional Urology in Shreveport, LA, reported that 70% of 77 non-coated prostheses bore a biofilm compared with 60% of 20 coated prostheses.

The rigor and thoroughness of the washout may be as important as or more important than any specific antibiotic or saline solutions used during washout, Dr. Henry explained.

"Perhaps the most important aspect of revision is to get a good mechanical cleansing of the capsule space. I think that is more important than the type of antibiotics being used. It is important to be aggressive in irrigating the space," he said.

Dr. Henry said he used a diluted combination of antibiotics, but noted that similar studies of surgical infection rates have shown that normal saline solutions can be as effective as antibiotic solutions.

To obtain the findings for the more recent study, presented at the AUA annual meeting in Chicago, the researchers prospectively obtained cultures from 20 clinically uninfected, antibiotic-coated, inflatable penile prostheses undergoing revision, primarily for mechanical failure such as tubing fracture or fluid loss. The standard coating on one model consists of a combination of rifampin and minocycline (InhibiZone, American Medical Systems, Minnetonka, MN), while a second model (Titan, Coloplast, Minneapolis) is coated with a substance that absorbs any antibiotic solution into which it is dipped.

There was no overt clinical evidence of infection at the time the procedures were conducted. The cultures were acquired as soon as a pump was exposed and additionally on any part displaying grossly visible biofilm.

The infection rate on the 20 coated prostheses was 60%. The infection rate on 77 non-coated prostheses in the earlier study was 70%. The primary infectious agent was a Staphylococcus genus that was present on 90% of the culture-positive non-coated prostheses and on 83% of the culture-positive coated prostheses. Three patients (3.5%) in the culture-positive non-coated group grew more than one culture isolate. None of the patients with antibiotic-coated prostheses cultured for more than one organism.

Although 73% of the procedures in this series were initiated to correct mechanical failure, Dr. Henry noted that mechanical failure rates are improving due to product enhancements.

The now-standard salvage lavage procedure was first described by Mulcahy et al (J Urol 1996; 155:155-7). It consists of complete removal of all components of the prostheses and foreign material associated with the implant. The corpora, reservoir pocket, and pump pocket are then irrigated in a stepwise fashion with a series of solutions. After the washout, gloves and instruments are changed, and new drapes are placed before the new prosthesis is handled and implanted.

In addition to a rigorous washout during the salvage procedure, Dr. Henry and study co-authors routinely initiate a 5- to 7-day course of oral quinolone therapy and a second antibiotic similar to amoxicillin/clavulanate prior to the procedure. This combination broadens antibiotic coverage. In response to a suggestion from a colleague outside the study, Dr. Henry now follows the operation with a 1-month course of oral quinolone.

Dr. Henry is an investigator for American Medical Systems and Coloplast.