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                      Tough TB Responds to Drug Treatment

   by Joe DeCapua

   An antibiotic used to treat severe infections shows promise against a
   very resistant and deadly form of tuberculosis. XDR-TB is resistant to
   at least four of the drugs used most often against the disease.
   Extensively drug resistant tuberculosis - or XDR-TB - is still
   considered rare, although cases have been reported in nearly 80
   countries. Health officials believe the number of XDR-TB cases is
   underreported because there's no specific test for it.
   It can be cured, but the odds against that happening are often quite
   high. It can kill quickly, especially if a person is co-infected with
   HIV, the virus that causes AIDS.
   Dr. Ray Chen, a staff clinician at the National Institute of Allergy
   and Infectious Diseases, says XDR-TB is the next step after MDR-TB, or
   multi-drug resistant tuberculosis, which is a lot more common.
   "That's been a known problem for many years, primarily as a result of
   people who don't take their drugs well. And then the tuberculosis bug
   slowly develops resistance to the drugs that are used," he said.
   MDR-TB is resistant to two of the top line drugs used for standard
   tuberculosis therapy. When the disease becomes resistant to two
   additional first-line drugs, it's upgraded to XDR-TB.
   "It came to world attention in 2006 in a study in South Africa where a
   number of patients were found to have this extensive resistance to
   tuberculosis drugs, and they had a very high mortality rate. And so it
   became recognized as a major problem for tuberculosis," he said.
   In fact, the mortality rate was as high at 90 percent in patients also
   infected with HIV.
   Standard TB treatment can take up to six months. MDR-TB treatment can
   last between 18 and 24 months.
   So researchers knew that more drugs were needed to tackle the various
   forms of TB.  They had heard of some informal studies using the drug
   linezolid on TB patients with some success. But there was no formal
   study.
   Linezolid is a drug that's already on the market and it's approved for
   the use of resistant bacteria, which we call gram-positive bacteria
   that don't respond to typical antibiotics.
   To find out, researchers tested linezolid on 41 patients with XDR-TB.
   The patients already had been treated for six months with the best TB
   drugs available, but failed to respond. Chen said linezolid was added
   to their regimen.
   "We found that adding the linezolid had a significant effect and that
   most of the patients converted their sputum from showing tuberculosis
   to not having tuberculosis in the sputum by six months. About 87
   percent of the patients became negative for tuberculosis within six
   months. So it showed a very good response," he said.
   That's the good news. The bad news is many of the patients suffered
   severe side effects. These include nerve problems with hands and feet
   going numb. There were also eye problems and abnormalities with red and
   white blood cells. Use of the drug was stopped before any of the
   patients suffered permanent damage.
   As a result, Chen said more studies are needed to determine whether it
   can safely be used on a large-scale in combination with other drugs. He
   also says new, potent antibiotics will be coming on the market and
   these may be tested on TB, as well.
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   [1]http://www.voanews.com/content/xdrtb-drg-22oct12/1530836.html

References

   1. http://www.voanews.com/content/xdrtb-drg-22oct12/1530836.html