Gilead Sciences Inc. (GILD) said the majority of certain hepatitis C genotype 1 patients it treated with its GS-7977 drug plus ribavirin had viral relapse within four weeks of completing 12 weeks of treatment, potentially putting into question the efficacy of the drug in some patients.
Shares were down 8.8% premarket at $50. As of Thursday's close, the stock has risen 34% since the start of 2012.
The biopharmaceutical last month completed its purchase of Pharmasset Inc. for more than $11 billion, in a deal expected to accelerate its hepatitis C drug pipeline. It said earlier this month that its GS-7977 drug--which it acquired in the deal--along with the older drug ribavirin, made hepatitis C undetectable after four weeks of treatment in all 10 patients with genotypes 2 and 3 treated. The trial was also the first to successfully eliminate interferon from the drug treatment. Interferon is a highly toxic, older hepatitis C drug with major side effects, and market watchers are keenly focused on drug developers finding ways to strip out that treatment from future hepatitis C regimens.
But, among eight genotype 1 patients treated, six experienced viral relapse. Two patients didn't, but they have only reached the two-week post-treatment time point. Those patients had a prior "null" response to an interferon-containing regimen.
"These data answer an important question about the use of GS-7977 and ribavirin for the treatment of genotype 1 null responder patients, suggesting that additional direct acting antivirals may be necessary to effectively treat this patient population," said Chief Scientific Officer Norbert Bischofberger. "We will continue to explore a number of therapeutic approaches to address this significant unmet medical need, including combinations with other oral antivirals."
Results from ongoing studies, including those involving genotype 1 treatment-native patients, will be released in the coming months.
Gilead earlier this month said its fourth-quarter earnings rose as the company's product sales continued to rise and it no longer booked deep reductions in royalties.
-By Ben Fox Rubin, Dow Jones Newswires; 212-416-3108; firstname.lastname@example.org