Ranbaxy Laboratories has withdrawn all of its generic versions of antiretroviral drugs from World Health Organization's list of approved HIV medicines, saying it's uncertain they are biologically the same as the patented drugs.

"Ranbaxy took action after it found discrepancies in the documentation about proof of bioequivalence of its generic drugs with the patented medicines," WHO said adding, the company plans to undertake new studies to establish their bioequivalence.

The company has already proposed dates to the UN health agency for submission of reports on new studies of the drugs, WHO said on Tuesday. The first study is expected to be completed by December.

The seven pre-qualified medicines Ranbaxy is withdrawing are: Indinavir 400 mg capsule, blister (60, 100), Lamivudine 150 mg tablet, blister (60,100), Lamivudine/Stavudine 150 mg/40 mg tablet, Al strip (10), 60 in box, Lamivudine/Stavudine 150 mg/30 mg tablet, Al strip (10), 60 in box, Nevirapine 200 mg tablet, blister (60, 00), Stavudine 30 mg capsule, Al strip (10), 60 in box, Zidovudine 300 mg tablet, blister (60, 100).

Earlier this year, WHO removed three other antiretroviral medicines manufactured by Ranbaxy and two more made by Cipla, from its list of prequalified products.

WHO said it removed these medicines from the list after inspections at the Contract Research Organizations revealed serious discrepancies between the original results compiled by the CROs and the results presented to the agency.