* Drug aims to prevent blood clots for those on chemotherapy
* FDA advisers say not clear which patients drug targets
By Anna Yukhananov
SILVER SPRING, Md., June 20 (Reuters) - French drugmaker Sanofi SA failed to win a U.S. advisory panel's support for an injection meant to prevent blood clots in certain cancer patients, making it unlikely the drug will be approved in the United States.
The panel of outside experts to the Food and Drug Administration voted 14 to 1, with one abstention, on Wednesday to recommend against approval of the semuloparin injection for cancer patients getting chemotherapy who are particularly at risk for blood clots.
The FDA usually follows panel recommendations, although it is not required to, and will make a final decision later.
Most panel members said the company had not done a good job of defining exactly which patients would benefit most from the drug, especially as those taking the medicine were also at higher risk of bleeding.
"Cancer patients have a lot to deal with just in treating their cancer with chemotherapy," said panel member Dr. Mikkael Sekeres, from the Cleveland Clinic Taussig Cancer Institute.
"When we add ... medicines to prevent complications, we have to be particularly careful in not adding harm," said Sekeres.
Sanofi has said cancer patients getting chemotherapy have a 6-1/2 times higher risk of getting blood clots than patients without cancer, and no other medicines are currently approved specifically to prevent the clots in patients on chemotherapy.
But FDA staff said approving an anti-clotting drug specifically designed for those on chemotherapy would change the practice of medicine, since groups that set cancer treatment guidelines only recommend such medicines in very specific situations.
They also doubted the clinical value of semuloparin, since only a small number of people who took the drug in clinical trials actually had issues with clotting, and most people died from other problems.
During the clinical trial, only 3.4 percent of people who took a placebo had a blood clot. At the same time, about 5 percent of patients died from other causes, raising doubts about the importance of preventing blood clots in cancer patients.
Semuloparin was also tied to a higher risk of bleeding compared with a placebo, with about one-fifth of patients having some bleeding issues while taking the drug, including bleeding into a critical area or organ.
Sanofi said it was disappointed with the panel's vote, given the lack of treatment options for cancer patients who want to prevent blood clots, known clinically as venous thromboembolism (VTE).
"Often clinically silent, VTE is a potentially life-threatening complication of cancer and its treatment that may increase morbidity, mortality and medical care and cost," the company said in a statement.
Sanofi's shares closed down 0.7 percent at 57.37 euros on the Paris stock exchange, compared with a 0.3 percent rise on the CAC 40 Index.