Medical humanitarian group Medecins Sans Frontieres (MSF) says India must stop its doctors prescribing "irrational" treatments to cure tuberculosis (TB), warning the practice is increasing drug-resistant strains of the disease.

India is already home to the highest number of TB sufferers globally with two million cases every year and drug-resistant strains are on the rise, MSF said in a statement ahead of World TB Day on Monday.

TB patients in India face a potentially "grave risk of developing drug-resistant TB due to irrational prescribing practices", MSF said.

While huge strides have been made in controlling TB worldwide, the emergence of deadly strains that cannot be cured with existing medicines has turned the illness into one of the globe's most urgent health concerns.

India's government has already said it is seeking to tackle deepening TB drug resistance with a wide-ranging national diagnostic and treatment programme for the communicable, airborne disease that usually attacks the lungs.

But MSF urged health authorities to go further and implement a "standardised first-line daily tuberculosis treatment regimen" in the public and private health sectors.

With public health care services overstretched, many TB patients turn to private doctors who have "never been trained to use TB drugs in a proper way", Leena Menghaney, India coordinator of MSF's Access Campaign, said.

MSF said some prescriptions are "completely inappropriate".

"When the patients get to us, they have become resistant to the drugs and it becomes far harder to treat them," Ms Menghaney said.

India, whose vast pharmaceutical industry churns out an ever-growing supply of copycat medicines to combat life-threatening diseases, has the largest private TB drug market.

There is "rampant proliferation" of TB drugs in a wide variety of dosages and combinations, and the emergence of drug-resistant strains in the country of 1.2 billion people is increasingly being linked to poor regulation, MSF said.

India's drug regulation is already under heavy fire from US authorities over another issue: worries about the quality of the country's medicines following a string of recalls.

Other countries have already taken steps to curb drug-resistant TB by ensuring drug regulators strictly regulate TB drugs in the private market, Ms Menghaney said.

"Governments like Brazil have even taken the additional step of making the public sector the primary distributor of all TB drugs," Ms Menghaney added.

TB is still the world's second most deadly infectious disease among adults, after HIV/AIDS, and every year kills 1.3 million people and causes nearly nine million to fall ill, according to UN figures.

While TB is curable, one third of those who have it - some 3 million people - do not get the treatment they need, often because they are poor.

The World Health Organization estimates India has 64,000 patients with drug-resistant TB.

"India can ill afford to delay" reforms in policies to treat TB, said Ms Menghaney, calling the number of drug-resistant TB cases in the country "alarming".

Some doctors have warned drug-resistant TB could spin out of control.

Before modern treatments were developed in the 1940s, TB killed two-thirds of sufferers.

AFP