(Reuters) - Idenix Pharmaceuticals Inc said it expects a delay in human trials of one of its experimental hepatitis C drugs after the U.S. Food and Drug Administration asked for additional safety data, sending its shares down 21 percent after the bell.
Clinical trials of the drug, codenamed IDX20963, has been put on hold until it provides a satisfactory response to the FDA, Idenix said in a statement.
Hepatitis C is an disease that affects the liver and if left untreated can lead to cirrhosis, cancer or need for a transplant.
In early February, the company stopped the development of two other hepatitis C drugs, IDX184 and IDX19368, after the FDA continued with a clinical hold, initiated following the death of a patient in a mid-stage trial conducted by Bristol-Myers Squibb Co using a similar compound.
"This signifies that the preclinical/clinical development of any nuc is likely even more challenging than anticipated," Oppenheimer & Co analyst David Ferreiro said in a note.
Idenix's hepatitis C drugs have been developed using a technology called polymerase inhibitors, or nucs. Nucs prevent the virus from multiplying and represent a new class of drugs for the disease.
IDX20963 belongs to a sub-class of nucs called uridine nucleotide, and the company has said previously that it is distinct from the two drugs whose development was stopped.
Ferreiro also noted that this setback occurred even when the drug -- a uridine analog is deemed safer than other nucs.
"Consequently, we continue to hold low expectations for IDX20963's ultimate success," he said.
Idenix shares were down at $4.03 in after-market trading. They closed at $5.13 on the Nasdaq on Thursday.
(Reporting by Pallavi Ail in Bangalore; Editing by Sriraj Kalluvila)