Antibiotic useful for localized treatment of bone wear

But Weiping Ren, M.D., Ph.D., associate professor of biomedical engineering in WSU's College of Engineering, has found a solution. Erythromycin can be administered directly at the site of bone breakdown, rather than orally, so the whole body is not affected. The details of Ren's study are published in the August 2011 issue of Clinical Orthopaedics and Related Research.

"Although oral erythromycin reportedly inhibits inflammation in patients with aseptic loosening, long-term systematic (oral) erythromycin treatment is not recommended," said Ren.

Used primarily for its antimicrobial properties, erythromycin is used to treat conditions like respiratory tract infections and whooping cough, both caused by harmful bacteria. In addition to fighting bacteria, erythromycin reduces inflammation, making it a successful treatment for aseptic loosening.

"But long-term systemic use of erythromycin raises concerns about various side effects, including bacterial resistance, liver damage and gastrointestinal discomfort," said Ren. "We hypothesized that it may be advantageous to restrict erythromycin delivery to the inflammatory tissue around the implant to avoid these side effects."

To test his idea, Ren implanted metal pins coated with erythromycin in the inflamed tissue surrounding the prosthetic joint. He measured bone growth and implant stability, both indicators of how well the prosthesis integrates with the bone, and analyzed microscopic images of the periprosthetic tissue -- the affected tissue surrounding the prosthesis.

Ren found that at very low doses -- about a quarter of the dose used for killing bacteria -- erythromycin effectively reduces aseptic loosening inflammation. "At the same time, we confirmed that oral erythromycin can be effectively delivered into the periprosthetic tissues, supporting our hypothesis that oral erythromycin can be used as one of the nonsurgical treatment methods to extend implant longevity," said Ren.

By extending implant longevity, localized erythromycin will safely treat aseptic loosening and reduce the likelihood that patients with the condition will need revision surgery. "Medical insurance costs will be greatly reduced, because revision surgery is much more expensive than primary surgery," said Ren.

Ren collaborated with David C. Markel, M.D., chairman of the Detroit Medical Center-Providence Hospital orthopaedic residency program and chief of orthopaedic surgery at Providence Hospital in Southfield, Mich.

The current study was funded by the Orthopaedic Research and Education Foundation. Ren also received funding through the Blue Cross Blue Shield of Michigan Foundation's McDevitt Excellence in Research Award for his 2009 study published in Bone.