The Medicines Co said it discontinued a mid-stage study of its experimental drug to reduce blood loss during surgery due to evidence of risk to patients.
Shares of the company fell 4 percent in extended trade, after closing at $26.64 on the Nasdaq on Thursday.
Medicines Co, known for its blood thinner Angiomax, did not disclose the nature of the safety issues.
The company said it is assessing all patient data from the study to determine the cause of the safety issues and any potential link to the drug.
The study testing the drug, codenamed MDCO-2010, had recruited 44 of a planned 90 patients in the first stage, the company said.
Medicines Co said it informed health regulators in Germany and Switzerland, where patients had been enrolled.
(Reporting By Vrinda Manocha in Bangalore; Editing by Sriraj Kalluvila)