NEW YORK (AP) -- A day after suspending sales of its cancer drug Iclusig, Ariad Pharmaceuticals said it has adopted a shareholder rights plan — often called a "poison pill" — a move that could help the company fend off a takeover.

Ariad said owners of its shares will be issued the right to buy one additional share for every share they own. The plan will go into effect if any person or entity buys a 4.99-percent stake in the company, or if an entity that owns a stake of more than 4.99 percent increases its holdings by at least half a percent.

Shareholder rights plans allow existing shareholders to acquire more stock at a discounted rate, and are typically used to discourage a takeover by an outside entity. They are designed to thwart anyone who buys a big chunk of its stock without board approval.

The Cambridge, Mass., company said it adopted the plan to protect $307.7 million in net operating loss carry forwards at the end of 2012 and $17.8 million in research tax credits. Those could be used to offset some of its taxable income or reduce tax liabilities. Ariad said its ability to use those credits would be reduced significantly if the company's ownership structure changes under tax law.

Shareholders will be able to vote on the plan at the company's annual meeting in 2014. The shareholder rights are scheduled to expire on Oct. 31, 2014.

Ariad's biggest shareholder is Sarissa Capital Management, a Connecticut-based hedge fund launched earlier this year by Alexander Denner, who previously was a health care executive with activist investor Carl Icahn. Sarissa disclosed holdings of 11.5-million shares, a 6.2-percent stake on Tuesday, purchased between Oct. 9 and Oct. 22.

Boston-based hedge fund Camber Capital Management LLC, which focuses on healthcare, also disclosed a stake of 10 million shares, or 5.4 percent, on Oct. 23, none of which was owned as recently as June 30, according to regulatory filings.

Ariad also said it is delaying its third-quarter report to the morning of Nov. 12. It was originally scheduled to post results on Nov. 6.

On Thursday Ariad suspended sales of its leukemia drug Iclusig because of heightened concerns that patients could suffer from life-threatening blood clots. The Food and Drug Administration says 48 percent of patients treated with the drug in an early-stage trial and 24 percent who took the drug in a mid-stage trial have suffered serious side effects, including heart attacks and strokes, and some patients died as a result.

Iclusig's label warns about those side effects, but in October Ariad said they were occurring at a higher rate than it had expected. The company said it wants to resume selling the drug and is talking to the FDA about ways to manage its risks.

Ariad Pharmaceuticals Inc. shares fell 44 percent to $2.20 on Thursday, down 87 percent from their closing price on Oct. 8.

The stock gained 18 cents, or 8.4 percent, to $2.38 in morning trading Friday.