By Bill Berkrot
(Reuters) - Vertex Pharmaceuticals Inc said U.S. health regulators placed a partial clinical hold on its mid-stage study of an experimental oral hepatitis C treatment because of potential liver problems, sending its shares sharply lower on Thursday.
Vertex said the U.S. Food and Drug Administration took the action on the Phase II study of its VX-135 in combination with the standard hepatitis drug ribavirin after elevated liver enzymes were observed in three patients taking the 400 milligram dose of its drug.
As a result of the hold, the U.S. biotechnology company said it was unable to evaluate results of the trial, even for those patients who had been getting the 200 mg dose of VX-135.
"We are committed to continuing to work closely with the FDA to provide the data needed to support evaluation of a 200 mg dose of VX-135 in the U.S.," Robert Kauffman, Vertex's chief medical officer, said in a statement.
The halted trial was being conducted in Europe. The 400 mg arm of the study was discontinued and the patients' liver enzymes returned to what they had been prior to entering the trial, Vertex said.
A U.S. study evaluating 100 mgs of VX-135 was not affected, the company said.
VX-135 is also being studied at 100 mg and 200 mg in combination with Bristol-Myers Squibb Co's daclatasvir, a highly promising hepatitis drug from a different class of oral medicines.
Vertex has the market leading hepatitis C treatment with Incivek. But that drug must be taken with the difficult to tolerate injected drug interferon to provide high cure rates.
Incivek sales have been declining sharply as patients wait for new all oral treatment regimens that promise very high cure rates without the need for interferon and the miserable flu-like symptoms that come with it.
The first of those are expected to become available in 2014 from other companies and Vertex has been playing catch-up.
"With our ongoing studies in the U.S., Europe and now New Zealand with VX-135 and daclatasvir, our strategy in hepatitis C is unchanged - to develop an all-oral therapy that provides a high cure rate across multiple hepatitis C genotypes," Kauffman said.
Vertex shares were down more than 9 percent at $80 in after hours trading after closing at $87.62 on Nasdaq.
(Reporting by Bill Berkrot; Editing by Grant McCool and Andre Grenon)