Shares in Ranbaxy, India’s largest generic drug maker, fell more than 10 per cent on Moday on news that US authorities had filed a court motion seeking documents and alleging the company sold adulterated products.

The report sparked investor concerns that it could derail a bid of up to $4.6bn by Daiichi Sankyo of Japan to buy Ranbaxy, although both companies said that the takeover would go ahead.