New York: Hyderabad-based Hetero Drugs Limited has become the second Indian pharmaceutical company after Ranbaxy to withdraw its anti-AIDS drugs from special World Health Organisation certification, saying that it is not certain about their bio equivalence with patented medicines.

The company, which is withdrawing generic versions of six antiretroviral drugs from the WHO's approved list of drugs for treatment of HIV/AIDS, told the UN health agency that the "centres" it had used for studies of bio equivalence were "incompatible with the current standards" and that there were "deficiencies" in the date submitted for the studies done, the WHO said.

Last week Ranbaxy had withdrawn its generic drugs for HIV/AIDS for similar reasons.

Hetero evaluated the Contract Research Organisations (CROs) it had used after receiving a warning letter sent by WHO to all manufacturers earlier this year and found them non-compliant with international standards of Good Clinical Practice and Good Laboratory Practice, the WHO said.

Hetero Drugs has committed to contact different CROs and submit new test results for the bio equivalence of the six medicines as soon as possible.

"Our findings, and the companies' admission of responsibility by withdrawing their products, show that CRO inspections are necessary," said Lembit Rago, Coordinator of Quality, Safety and Efficacy of Medicines at the WHO.

"Current WHO procedures are ultimately improving medicines monitoring mechanisms which will, in the long term, ensure better quality treatment for patients."