UPDATE 1-FDA panel votes against approval of Medicines Co's blood clot preventer
* Panel votes 7-2 against drug's use during a heart procedure
* Panel votes 9-0 against drug's use in patients with stents
* Panelists cite lack of data to prove drug's efficacy
* Shares fall 12 percent in after-hours trading (Adds details, analyst comments)
Feb 12 (Reuters) - An independent advisory panel to the U.S. Food and Drug Administration said a blood clot preventer developed by The Medicines Co should not be approved due to a lack of data to prove its efficacy.
Medicines Co shares fell 12 percent to $29.05 in post-market trading. Regular trading had been halted on Wednesday ahead of the panel meeting.
The panel voted 7-2 against approving the drug, cangrelor, for use during angioplasty - a heart surgery for widening narrow or clogged arteries.
The panelists also voted unanimously against allowing cangrelor's use in patients with stents, who are at an increased risk of events such as stent thrombosis - a blood clot that forms at the site of the stent.
Panelists said they were not convinced that data from an 11,000-patient trial was enough to prove cangrelor's efficacy, especially given the failure of two prior trials.
"I am not sure if it could count as a pivotal trial," said Scott Emerson, a panel member and a professor of biostatistics with the University of Washington.
The trial, named Champion-Phoenix, had shown that those on cangrelor had a reduction in the combined risk of death, heart attack, repeat procedure or stent thrombosis.
The two failed late-stage trials were stopped in mid-2010 after data showed that the drug was ineffective.
The company had tweaked the study design for the latest trial to differentiate between heart attacks associated with the drug and those that may have been associated with the procedure.
The Champion-Phoenix trial was testing cangrelor against a rival drug, Plavix, made by Bristol-Myers Squibb Co. Plavix is generically known as clopidogrel.
"I don't think they are going to develop cangrelor further. Because they would have to run another 10,000-15,000 patient study," Jefferies analyst Biren Amin said.
Amin said there is probably very little prospect for the drug at least in the United States.
"They could try to file in Europe and try to get approval. That is still a potential," he said.
He had expected the drug to reach U.S. sales of $224 million by 2020.
In briefing documents put out ahead of the meeting, FDA's medical team leader Thomas Marciniak recommended on Monday that cangrelor not be approved, saying data on the drug did not show it was as good as or superior to a rival drug.
A U.S. consumer group also urged the FDA to reject cangrelor, citing ethical issues with the way the company conducted the trials.
Public Citizen alleged that many patients on the trial received clopidogrel - usually given before cardiac stent procedures to prevent clot formation - after the procedure, likely resulting in a larger number of clots and heart attacks.
(Reporting by Esha Dey in Bangalore; Editing by Sriraj Kalluvila)