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New Antibiotic Shows Promise Against TB

Doctors have known how to treat tuberculosis for more than 50 years, yet it remains one of the world's great killer diseases. There are more than 9 million new cases of TB worldwide and a million and a half people die of the disease each year. About 90 percent of those cases take place in the developing world, and TB is the leading cause of death for patients with AIDS.

Yet, there is little research into new medications to fight TB. According to Doctor Richard Chaisson, a professor at the Johns Hopkins Medical School, that's largely because pharmaceutical companies don't see a profitable market for tuberculosis drugs.

"The current treatment for tuberculosis has been around for 35 years and we know that while it's good, it's not good enough," he says. "We're looking for new treatments for TB that will shorten the time that it takes to cure people so that more people can be treated with scarce health resources around the world and to have drugs that work against resistant strains of TB that have arisen in recent years."

Chaisson and colleagues at Hopkins and in Brazil have been examining a new antibiotic that they believe has TB fighting potential. Moxifloxacin came onto the market about eight years ago, and has been used to treat other respiratory diseases.

The researchers tested moxifloxacin and found the drug could kill TB in the lab. Now, they have tested it on close to 200 TB patients in Brazil. They found those on moxifloxacin had a better and faster response than patients getting standard treatments. "Within a week we saw the differences," Chaisson says. "And by the end of two months of treatment we've found that the patients on moxifloxacin were significantly more likely to have responded to the treatment, that is, they were no longer growing TB from their lungs. It was about 25% higher cure rate at that point with moxifloxacin than with the standard treatment."

Another positive finding was that moxifloxacin had few side effects. Chaisson admits his team was worried about toxicity, because until they began their study, patients given moxifloxacin for other infections took the medicine for a week, or at most 10 days. "We gave it for eight weeks and there was some worry that maybe when you give this drug for eight weeks there will be side effects that we hadn't previously seen. But fortunately there weren't any."

The biggest expense in treating TB is the cost of doctors and nurses to monitor patients over the typical six-month course of therapy, not the cost of medications. Even so, the drug's manufacturer, Bayer, has agreed that if moxifloxacin proves to be effective against tuberculosis, the company will provide the drug at a much-reduced rate to TB patients.

Chaisson and his colleagues are now proceeding with a larger scale study on the effectiveness of moxifloxacin and expect to have results in the next year or so.

Chaisson's research was funded by a U.S. government program that focuses on so-called 'orphan diseases' — diseases that drug companies generally do not have an interest in.

He presented his research recently at the Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago.