Baxter Healthcare Corp., which produces about 50% of the heparin drug sold in the U.S., has halted the production of the drug’s multi-dose injectable form, following reports of serious allergic reactions in several patients. The death of four patients may also be linked to the drug.

The FDA said that most of the reactions, such as breathing difficulty, excessive sweating, nausea and falling blood pressure, had been in patients receiving a high dose. Heparin is a blood thinner used to prevent blood clots in patients undergoing kidney dialysis and heart surgery.