WASHINGTON (AP) — Scientists are hot on the trail of a new tuberculosis treatment that a small study suggests might one day offer an alternative to battle this deadly lung disease, even if it's resistant to today's two main drugs.

There haven't been new medications to treat TB in four decades. But the experimental three-drug combination, revealed Monday at the International AIDS Conference, is one of a list of promising compounds under intense testing around the world.

"We are cautiously optimistic that we are at the dawn of a new era for TB drugs," Dr. Diane Havlir of the University of California, San Francisco, who is co-chairing the meeting, told The Associated Press. She wasn't involved with the new research.

TB is one of the world's oldest killers, and every year it claims the lives of more than 1.5 million people, mostly in developing countries. It's also the leading killer of people with AIDS.

Standard first-line treatment requires taking four medications for six months. A frightening factor is that the bacteria that cause TB are fast becoming impervious to the two main drugs in that cocktail. The World Health Organization estimates there are more than 650,000 cases of multidrug-resistant TB a year. Treating drug-resistant TB can take more than two years, if it works at all.

Enter the new drug research.

Scientists in South Africa divided 85 newly diagnosed TB patients to take a variety of combinations of standard or experimental TB drugs,

Fifteen of the patients received a unique trio that emerged as the study's focus: An experimental antibiotic code-named PA-824, along with the pneumonia drug moxifloxacin and an older TB drug, pyrazinamide.

In a two-week test, the drug trio killed at least as much of the TB bacteria that patients coughed up as today's standard four-drug therapy, and possibly worked a bit faster, said Dr. Mel Spigelam of the nonprofit TB Alliance, the Global Alliance for TB Drug Development. Continued...