THURSDAY, Feb. 26 (HealthDay News) -- Combination treatment with two FDA-approved drugs shows promise in treating extensively drug-resistant tuberculosis (XDR-TB), a U.S. study shows.

In laboratory tests, researchers at the Albert Einstein College of Medicine and the National Institute of Allergy and Infectious Diseases found that a combination of the drugs clavulanate and meropenem inhibited the growth of 13 XDR-TB strains. The combination treatment was also effective against normal TB. Both drugs are approved in the United States for treating other bacterial infections in adults and children.

The study was published in the Feb. 27 issue of Science.

Current therapy for normal TB requires four antibiotics that must be taken for at least six months. XDR-TB is resistant to at least four of the drugs used to treat TB. The cure rate for patients with XDR-TB is 12 percent to 60 percent.

"If proven in human subjects, the ability to simplify treatment to just two drugs that work against drug-susceptible [TB], multi-drug-resistant [TB] and XDR-TB could help patients better adhere to therapy," study senior author John S. Blanchard, a professor of biochemistry at Einstein, said in a college news release.

"This discovery could be one of the most promising developments in TB research since the discovery of isoniazid -- it is very exciting," William Jacobs, a professor of microbiology and immunology at Einstein and associate director of the Einstein-Montefiore Center for AIDS Research, said in the news release. Isoniazid, the first effective anti-tuberculosis medication, was discovered in the 1950s.

Plans are under way for clinical studies in Korea and in South Africa to determine whether the combination treatment is effective in patients with XDR-TB.

This highly dangerous form of TB is rare in the United States, with only 83 documented cases in the country between 1993 and 2007. However, XDR-TB is emerging as a serious problem in some developing nations.

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