A panel of federal health advisers on Wednesday voted against approval of the Medicines Co.'s anti-clotting drug cangrelor.

The Food and Drug Administration's panel of heart experts voted 7-2 against recommending the drug to prevent blood clots in patients who have undergone surgical stenting procedures to open narrowed or blocked coronary arteries. Panelists said there were too many design problems and inconsistencies in the company's studies.

The FDA is not required to follow the advice of its panelists, though it often does.

Medicines Co. submitted the drug based on an 11,000-patient study showing cangrelor lowered the rate of blood clots and heart attacks in the first 48 hours after surgery compared with Plavix, the standard blood-thinning drug. But two earlier studies of the drug failed to show any advantage and linked cangrelor to more bleeding problems.

The FDA's lead reviewer on the drug, Thomas Marciniak, published a strikingly negative review of the company's three studies ahead of the meeting. Marciniak argued that patients did not receive Plavix at appropriate times and doses, exposing them to unnecessary risks and distorting the trial findings.

Panelists noted there are already other next-generation blood thinners on the market, such as Eli Lilly & Co.'s Effient, available to physicians.

Wall Street analysts generally have low sales expectations for cangrelor, assuming it ultimately wins approval. Leerink Partners analyst Joseph Schwartz said in a note earlier this week he thinks cangrelor will have peak sales of $200 million annually.

Based in Parsippany, N.J., the Medicines Company's main approved product is the the anti-clotting injection Angiomax.

Shares of Medicines Co. were halted in trading Wednesday pending the panel vote.