DAIICHI Sankyo Co, Japan's third-biggest drug maker, stuck to a 198-billion-rupee (US$4.1 billion) bid for Ranbaxy Laboratories Ltd, even as the Indian company's market capitalization fell to one-third of the June offer.

Daiichi Sankyo Co fell the most on record in Tokyo trading yesterday on concern it will book acquisition-related losses. Ranbaxy sank to as low as 236 rupees in Mumbai yesterday, 68 percent below the June 11 offer price of 737 rupees a share.

"The price of 737 rupees is fixed," Daiichi Sankyo Chief Executive Officer Takashi Shoda said yesterday in Tokyo.

"If Ranbaxy's stock price continues to move this way, we will follow accounting standards and consult with our accountants to determine valuation losses."

Daiichi Sankyo, which sells hypertension drug Benicar, agreed to buy the Indian company to enter the market for generic drugs, where sales are growing almost twice as fast as demand for branded medicines. Ranbaxy's stock price has slumped as regulators in United States probe the company and stock markets fall worldwide.

Daiichi Sankyo tumbled 375 yen (US$3.76), or 15 percent, to 2,190 yen on the Tokyo Stock Exchange, the steepest decline since Sankyo Co bought Daiichi Pharmaceutical Co in 2005. It was the sharpest drop among the 33 companies that comprise Japan's Topix Pharmaceutical Index.

The US is probing whether Ranbaxy destroyed reports it was required to keep, falsified data and failed to meet quality-control specifications in manufacturing the generic drugs it sells. The Indian company has denied the allegations.