PARSIPPANY, N.J. (AP) — Medicines Co. said Wednesday it stopped late-stage testing of cangrelor, an anti-clotting drug candidate, because it was not meeting its goals in two clinical trials. Medicines Co. has been conducting late-stage studies for more than three years, testing cangrelor's ability to prevent blood clots in patients who have had angioplasties to clear blocked arteries. An independent monitoring committee said cangrelor did not appear to be more effective than Plavix, an older drug, and did not appear equally effective or more effective than standard treatments alone. Medicines Co. shares plunged on the news, losing almost half their value in premarket trading. The stock fell to $5.95 — which would represent a seven-year low — after closing at $11.14 Tuesday. The monitoring committee recommended that Medicines Co. stop enrolling patients in both trials and examine all the data. It said the drug might be more effective when used for a shorter time when oral drugs can't be used. The company said it plans to step up testing of cangrelor in that setting. The monitoring committee said a trial called Champion-Platform trial would not meet its goal. The trial was intended to compare a combination of cangrelor and standard treatment to standard treatment alone, and Medicines Co. hoped it would show cangrelor was as effective or better than those drugs at preventing clotting. The committee also said cangrelor was not significantly more effective than Plavix in a study called Champion-PCI. Plavix, or clopidogrel, is sold by Sanofi-Aventis of France, and is one of the world's top drugs by revenue. Medicines Co. said it plans to enroll 200 patients in a study called Bridge, which is intended to show the drug significantly reduces the buildup of platelets over five days. The trial will involve patients who stop taking clopidogrel as they prepare for heart surgery. It planned to enroll more than 15,000 patients in the two late-stage studies.