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 bioequivalence 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Last week Ranbaxy had withdrawn its generic drugs for HIV/AIDS for similar reasons.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 it had used after receiving a warning letter from 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 bioequivalence 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."
Ongoing WHO inspections of CROs conducting tests on anti-retrovirals are part of the continuing monitoring process and an integral component of the pre-qualification work.
This work reflects WHO's responsibility to assist countries in promoting quality medicines and improving their quality assurance mechanisms, the agency said.
The irregularities found during the CRO inspections, the WHO said, do not undermine the proven pharmaceutical quality of the medicines, "including their purity and stability", but show that not all CROs can be relied upon as a source of evidence on the medicines' bioequivalence with their originator products.
Bioequivalence tests are conducted in volunteers whose blood is tested after receiving treatment with the medicine, to determine whether the blood concentration of the generic drug is similar to that of the originator product.
The current WHO list of pre-qualified medicines contains 48 anti-retrovirals, including a triple fixed dose combination (a three-in-one pill) manufactured by Cipla.
WHO's advice to countries is that, in principle, patients should suspend the use of de-listed medicines and switch to other pre-qualified products. However, if it is difficult to obtain alternative pre-qualified products immediately, it is recommended that patients continue the use of de-listed products.
The risk of withholding treatment is higher than that of providing medicines whose bioequivalence is not proven but which have demonstrated quality and safety.
A switch to non-prequalified products is not recommended, as their quality has not been documented by WHO.