On BSE, the stock opened at Rs 685 and slumped 4.25 per cent to Rs 665.35. At 1200 hours, it was trading at Rs 674.45, down 2.94 per cent from the previous close.
The scrip opened at Rs 683.85 on NSE and went down by 4.34 per cent to Rs 664.10. At 1200 hours, it was trading at Rs 673.35, down 3.01 per cent.
According to news reports, 20 US states have filed a suit in a US district court against six drug manufacturers, including Aurobindo Pharma, for purported price manipulation of doxycycline hyclate, an antibiotic, and glyburide, a drug used for treatment of diabetes.
The benchmark Sensex was trading at 26,470.88, down 0.18 per cent, from its previous close.