Gilead Sciences Inc's shares fell as much as 10 percent, after the drug maker forecast bleak sales for its hepatitis C drugs this year, underscoring the need for the company to strengthen its pipeline through acquisitions.

Sales of the drugs, including Sovaldi and Harvoni, have slowed, missing Wall Street estimates in the past few quarters, but still account for nearly half of Gilead's total revenue.

Chief Executive John Milligan acknowledged on Tuesday that the company had few prospects for new products over the next few years. "It makes it challenging for us to grow without an acquisition," Milligan said.

Several analysts said Milligan's stance reflected a change in the company's M&A strategy.

"We continue to see M&A as the primary catalyst though the level of urgency for deals is under-recognized," Barclays analysts said.

Gilead is one of the few large drugmakers to have eschewed splurging on multi-billion dollar deals in the recent past even as M&A activity in the healthcare sector hit record levels.

The company had $32.4 billion of cash, cash equivalents and marketable securities as of Dec. 31.

At least 2 brokerages downgraded their ratings on the stock, while 10 cut their price targets.

"Management desperately needs to identify candidates for Gilead's pipeline capable of changing the conversation among investors from 'How bad will it get?' to 'How good could it be?'," Cowen analysts said.

Gilead forecast 2017 hepatitis C drug sales of $7.5 billion-$9 billion, much lower than the $12 billion Wall Street analysts had expected, due to fewer patients starting on treatments and increased competition.

Hepatitis C, estimated to infect about 3.2 million Americans, is a viral disease that causes inflammation of the liver that can lead to liver failure.

Sovaldi and Harvoni revolutionized treatment of the disease, helping triple the company's sales to nearly $33 billion in 2015 from 2013.

Despite the recent slowdown in sales of hep C drugs, analysts remain largely bullish on the stock. Seventeen of 29 analysts rate the stock "buy" or higher and rest have "hold" ratings, according to Thomson Reuters data.

Gilead's shares were down 9.5 percent at $66.18 on Wednesday, after hitting a near three-year low of $65.75. The stock was the biggest drag on the S&P 500 Index.

"We are still of the view that Gilead can buy growth or an impactful pipeline or both, but investor patience seems to be wearing thin," Barclays analysts said.