The Food and Drug Administration announced today that it has approved Johnson & Johnson's (JNJ -0.69%) tuberculosis drug Sirturo, the first drug to gain approval from the agency in 40 years that tackles the disease using a new mechanism of action..

Sirturo will be used as part of a combination therapy to treat adults infected with bacteria that are resistant to other drugs. The drug was approved based on just two phase 2 trials because of the unmet need for new antibiotics. In one trial, the drug cut the median time for treatment to 83 days, compared to 125 days for patients that received placebo.

Most of the potential patients reside outside the U.S. -- in 2011, there were only 10,528 patients that became sick with tuberculosis in the U.S., compared to 9 million worldwide -- and the drug will only be used on the subset of those who won't respond to currently available treatments because of potential side effects. The drug can affect the heart's electrical activity, which can lead to issues with heart rhythm. There were also more deaths in the Sirturo-treated group than the group treated with placebo, although it wasn't clear that the drug was the cause.

Sirturo, manufactured by Janssen Therapeutics, was approved under the FDA's accelerated approval program, which provides patients earlier access to promising new drugs while the company conducts additional studies to confirm the drug’s clinical benefit and safe use. The drug was given fast-track designation, priority review, and orphan-product designation as it "demonstrated the potential to fill an unmet medical need, has the potential to provide safe and effective treatment where no satisfactory alternative therapy exists, and is intended to treat a rare disease," said the FDA.

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