The drug, known as BMS-986094, was acquired by Bristol earlier this year through its $2.5 billion purchase of Inhibitex Inc. It belongs to a promising new class of hepatitis C drugs known as nucleotide polymerase inhibitors, or nucs.

The mid-stage trial was halted early this month after the initial case of heart failure, which subsequently resulted in death.

Bristol said it was working closely with the U.S. Food and Drug Administration and trial investigators to follow up on all patients in the trial, nine of whom have been hospitalized.

The company said two patients remain hospitalized, citing issues of heart and kidney toxicity.

"We will also work expeditiously to share the results of our further investigations more broadly in the medical and scientific community," Elliott Sigal, Bristol's chief scientific officer, said in a statement.

The FDA last week placed a partial hold on a trial of Idenix Pharmaceuticals Inc's experimental hepatitis C drug, citing the heart-related problems seen with Bristol's compound.

Shares of Bristol, which closed at $32.15 on the New York Stock Exchange, were trading at $32.18 after hours. Shares of Idenix, which closed at $6.09, were down 6 percent at $5.74 after hours.

Hepatitis C, which is transmitted through the blood, kills more than 15,000 Americans each year, mostly from illnesses such as cirrhosis and liver cancer.

The Centers for Disease Control and Prevention recently called for all baby boomers to be tested for the disease, especially in light of newly available therapies that can cure around 75 percent of infections.

The field has attracted broad interest with two new hepatitis C drugs, Incivek from Vertex Pharmaceuticals Inc and Merck & Co's Victrelis, reaching the U.S. market in the past year.

Along with Bristol and Idenix, companies aiming to improve on existing treatments by developing pill-only regimens to combat the virus include Gilead Sciences Inc and Vertex.

(Reporting By Deena Beasley; Editing by Tim Dobbyn and M.D. Golan)

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