Updated from 9:21 a.m. EDT

The Medicines Company

(MDCO) - Get Report

announced it was ending two trials of an anti-clotting drug, a project the company has been working on for three years, sending shares deep into the red.

The drugmaker said the clinical trials of cangrelor were not meeting the goals of being as or more effective than Plavix, an older drug used to prevent blood clots in patients who have had angioplasties to clear blocked arteries.

The news sent shares plunging 42.6% to $6.40 in recent trading.

Medicines will save about $5 million this year through the discontinuation.

Copyright 2009 TheStreet.com Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed. AP contributed to this report.