Pfizer antibiotic may bring re-infections according to a study
Wednesday, September 27, 2006, 07:42
Pfizer Inc.'s Zithromax antibiotic may quadruple the risk of being re-infected with a potentially blinding eye infection that the drug is intended to treat, researchers said. While Zithromax worked against the initial outbreak of the infection, called trachoma, those taking the drug were more likely to be re-infected than those treated with surgery alone, said a study published yesterday in the Journal of the American Medical Association. The antibiotic appeared to blunt the immune system's ability to develop natural resistance by shortening exposure to the bacteria, the study said. „This is like the law of unintended consequences,” said Deborah Dean, co-author of the paper and a researcher at Children's Hospital Oakland Research Institute who is working on a vaccine for Trachoma. Zithromax, also available in generic forms, „wipes out the infection and your immune system has barely had time to get going.” Trachoma is the second-most frequent cause of blindness. The study should encourage efforts to find a vaccine for trachoma since antibiotics don't appear to treat the long-term problem, Dean said. About 80 million people, most in developing countries, are infected, and 8 million have been blinded or lost some vision, according to the International Trachoma Initiative. At least one other study has shown that Zithromax may do more harm than good by hampering the body's ability to fight off future infections, Dean said. A 2005 study found that sexually transmitted Chlamydia infections initially dropped after patients used Zithromax, then increased because of susceptibility to re-infection.
Pfizer infectious disease researcher Charles Knirsch said he is skeptical of the paper's conclusion related to natural immunity because the researchers didn't provide evidence to support that finding. He said there is no good way to test to determine whether someone has developed immunity to trachoma. The higher recurrence of infections among a certain group might be explained by geographical location, he said. Other studies, including one on patients in Morocco, showed that treating the entire population with Zithromax almost wipes out the disease, Knirsch said. „The solution isn't to wait 15, 20 years for a vaccine to come along,” Knirsch said. “The solution is to treat 100% of the community and eliminate this blinding disease.”
Pliva d.d., based in Zagreb, Croatia, makes a generic copy of Zithromax, as do Basel, Switzerland-based Novartis AG, and Petah Tikva, Israel-based Teva Pharmaceutical Industries Ltd. Trachoma infects the inside of the eyelid, and scaring builds up over time that makes the eyelashes turn inward. Eventually the eyelashes start scratching the surface of the eye, allowing bacteria to get into the eye and leading to blindness. The study was funded by the New York-based International Trachoma Initiative and the National Institutes of Health in Bethesda, Maryland. (Bloomberg)