NEW YORK (AP) — Ariad Pharmaceuticals is suspending sales of its leukemia drug Iclusig because of concerns that patients could suffer from blood clots. The said Thursday that the Food and Drug Administration asked it to stop marketing the drug Wednesday afternoon. The company is negotiating with the FDA about changes to prescribing information and new ways to manage the risks associated with Iclusig. Ariad said it wants to resume marketing the drug.

Shares of Ariad Pharmaceuticals Inc. have lost three-quarters of their value, trading at their lowest level in three years, since concerns about side effects were disclosed earlier this month. The stock slid 43 percent to $2.24 in premarket trading Thursday. In December the FDA approved Iclusig as a treatment for two rare types of leukemia. It’s a daily pill and Ariad’s only approved product. It brought in $13.9 million in sales in the second quarter.

On October 9 the company disclosed a higher rate of side effects from Iclusig related to blood clots. Ariad said that after two years of research in a study, 11.8 percent of patients treated with the drug suffered a serious blood clot in an artery, worsening from the eight percent rate after 11 months. The FDA halted enrollment of patients in new studies, and on October 18 Ariad said it is ending a late-stage trial of the drug because of those side effects.