Drug-resistant TB risk demands push for new drugs

• Infections • May 20, 10

Multi-drug resistant strains of tuberculosis (TB) could become dominant forms of the disease in the next few decades, adding heavy financial and medical burdens to already struggling health systems, doctors said on Wednesday.

In a series of studies into TB, scientists said “superbug” strains of the disease were already gaining ground in some countries and called for greater investment into research and development of new drugs and possible vaccines.

Multidrug-resistant tuberculosis, known as MDR-TB, has much lower cure rates, higher death rates, and costs far more to treat than normal TB, they warned.

An estimated 440,000 MDR-TB infections occurred around the world in 2008, accounting for 3.6 percent of known cases.

Neel Gandhi of New York’s Yeshiva University and Paul Nunn of the World Health Organisation in Geneva, who conducted one of the studies, found that India and China had around 50 percent of the global MDR-TB burden, followed by Russia with 9 percent.

“Unless countries invest substantially in management of MDR TB, the possibility remains that MDR strains could become the dominant form,” they wrote.

“The future possibility of strains that are totally resistant to all anti-tuberculosis drugs is not inconceivable.”

TB—which causes around 1.8 million deaths worldwide every year, or nearly 5,000 people a day—is often associated with poverty and is one of the leading causes of death among people in economically productive age-groups in developing nations.

Of a 11 million active cases of TB recording in 2008, 95 percent of cases were in low- and middle-income countries.

It is caused by the Mycobacterium tuberculosis bacteria and can be cured with antibiotics, but they must be taken daily for months to be effective and public health funding cuts in some countries may mean fewer drugs are available.

Because people do not always take the drugs properly, MDR-TB strains are starting to take hold and the WHO says there is an urgent need for countries to set up laboratories to fight it.

Gandhi and Nunn said MDR-TB treatment is less effective, requiring 24 months of treatment rather than the usual 6 months, and far more expensive—costing an average of $3,500 in drugs per patient versus around $20 per patient for normal cases.

“Even though there are fewer cases of drug-resistant TB, the cost and complexity of their management place a significantly greater burden on the health system,” they said.

In other studies in the series, which was published by The Lancet on Wednesday, scientists said the combined impact of new drugs, vaccines, and diagnostic tests could cut worldwide incidence of TB by 94 percent by 2050, but the investment needed to bring this about it falling way too short.

Only around a quarter of the funding needed is being put into TB drug research and development, they said, and called for new ways of encouraging pharmaceutical firms into the field.

“Development of new drugs for TB is lengthy, expensive, and risky, and the expected revenues are too small to justify commercial investment,” wrote Zhenkun Ma of the Global Alliance for TB Drug Development. “New financing and market incentive mechanisms are needed.”

According to the studies, there are 11 potential TB vaccines being tested in human trials and up to 10 experimental medicines in the TB drug “pipeline”. Since many drugs fail in late-stage trials, this handful of possibilities is unlikely to be enough.

“To eliminate TB as a public health concern by 2050, all responsible parties need to work together to strengthen the global anti-tuberculosis drug pipeline,” the scientists said.

SOURCE: http://www.thelancet.com/series/tuberculosis The Lancet, online May 19, 2010.