On Monday, India added the first new drug in 50 years to its existing cocktail of free medications prescribed under its public health programme to treat the extensively drug-resistant tuberculosis (XDR TB), which defies cure. But adding a new drug, in this case the World Health Organisation-approved bedaquiline, will not stamp out XDR TB unless the health ministry comes down hard on doctors who treat people symptomatically and prescribe TB drugs without diagnosis.

Adding the new drug, however potent, will treat the infection for a while, but at a cost. Even without bedaquiline, treating XDR TB involves giving the patient a cocktail of 12-15 drugs and daily injections that cause toxic side effects. Even when this expensive drug is given for free, many patients stop treatment midway because it needs to be taken daily for 20 months or more, and is too toxic. According to WHO data, globally, less than half of all patients who start MDR-TB therapy are treated successfully.

Like with all microbial resistance, the tuberculosis bacterium develops resistance when the medicines used to treat TB are misused or mismanaged; when patients stop taking medicines before the full course of treatment; when doctors prescribe the wrong medicines, dose or duration; when people do not take their TB drugs regularly; or when a person is directly infected.