A drug that costs just two cents for a daily dose can treat tuberculosis (TB), even a drug-resistant form of the disease, new research says.

The drug, oxyphenbutazone (trade name Tandearil), can fight persistent tuberculosis but researchers fear the drug will probably never be studied in a proper clinical setting because no drug company will want to sponsor a trial that would not yield any profits. The drug is off-patent and is used as an anti-inflammatory drug.

"It is difficult today to launch clinical studies on a medication that is so outdated in the United States, that it is mainly used here in veterinary medicine to ease pain. No drug firm will pay for clinical trials if they don't expect to make a profit on the agent. And that would be the case for an off-patent drug that people can buy over the counter for pain in most of the world," said the study's senior author, Dr. Carl Nathan, from Weill Cornell Medical College in New York.

Researchers say that the drug should be used for common pain but added that the drug's side effects were less compared to other drugs used to treat TB.

In 1993, World health Organization (WHO) had declared TB as a global public health emergency. According to a more recent report by the agency, in 2010 there were 8.8 million people in the world who were diagnosed with TB. In the same year, as many as 650,000 people were diagnosed with multi-drug-resistant tuberculosis (MDR-TB).

A recent study had said that one in ten cases of TB is drug-resistant, meaning that these cases don't respond to standard therapy, thus requiring drugs that are stronger, more expensive and cause many side effects. The problem is that the bacterium that causes TB can hide out in the body even during the long treatment and can reemerge later.

Researchers in the present study tested drugs that are used to treat hidden TB in the body. They identified four conditions where the pathogen becomes dormant in the body: low oxygen, mild acidity, a fat instead of sugar to eat and a small amount of the natural defense molecule nitric oxide.

Researchers methodically tested 5,600 drugs in a test tube and found that oxyphenbutazone was better at fighting TB bacterium. They found that the conditions that make the bacterium dormant in the body, changes the drug to a form where it starts killing the bacterium both alive and dormant.

The drug cannot be tested on mice because mice break down the drug faster than humans.

"This makes testing the drug for TB use in humans problematic since the FDA requires preclinical animal testing studies for safety and efficacy. Yet there is a long track record of oxyphenbutazone's relatively safe use in hundreds of thousands of people over decades," Dr. Nathan said.

Another drug and same story

The research team found another drug, Nitazoxanide, which can act against TB but is still patented for use against infections caused by other pathogens. This drug too is metabolized faster in mice making it unfit for a pre-human drug trial.

The study was published in the journal PNAS.