NEW YORK (AP) — Shares of Medicines Co. fell Monday on worries about critical comments on its anti-clotting drug cangrelor by a Food and Drug Administration investigator.

Thomas Marciniak wrote that he feels cangrelor shouldn't be approved for patients who are undergoing an angioplasty, a procedure that is used to open narrowed or blocked coronary arteries. Marciniak said he has concerns about the way studies of the drug were run, and he said cangrelor doesn't appear to work better than an older drug, Plavix, or standard treatments.

A panel of FDA advisors will discuss cangrelor on Wednesday, and documents related to the meeting were posted on the agency website Monday.

The panelists will make a recommendation for or against approval of the drug. The FDA isn't required to follow the advice, but it often does so.

Medicines Co. CEO Clive Meanwell said the FDA will take a thorough look at cangrelor and the questions on the agency's website are mixed, as not all the reviewers are focusing on the same issues.

Leerink Partners analyst Joseph Schwartz said the panel documents were "more critical than expected," but Schwartz said he has fairly low expectations for cangrelor and believes Medicines Co. should be able to meet its long-term revenue goals even if cangrelor isn't approved. He thinks sales of the drug would peak at about $200 million per year.

In January 2013, Medicines Co. said cangrelor met its goal in a late-stage clinical trial that involved about 10,900 patients. The company said in the first 48 hours after surgery, patients who took cangrelor were less likely to die or suffer a heart attack than patients who took Plavix.

However the drug failed in two other late-stage trials. The Parsippany, N.J., company stopped those trials in 2009 because a monitoring panel said the drug wasn't going to meet its goals.

Shares of Medicines Co. lost $1.49, or 4.4 percent, to $32.73 in afternoon trading. The stock had gained about 13.5 percent over the past 12 months.