Piling on the Phase 3 Data

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Gilead Sciences  is piling on the phase 3 data for its hepatitis C drug sofosbuvir, announcing two more successful trials for the drug formerly known as GS-7977.

At this point, it looks extremely likely that sofosbuvir will be approved by the FDA. Previous data, released last November, showed the drug worked in patients with genotype 2 or 3 hepatitis C virus. Gilead now has data showing the drug works on genotypes 1 through 6.

In the Neutrino trial, patients with genotype 1, 4, 5, or 6 hepatitis C infection were treated with sofosbuvir combined with ribavirin and Roche's Pegasys for 12 weeks, which cured 90% of patients for the mixed population and 89% when you just look at genotype 1. Typically, ribavirin and Pegasys alone would produce a cure rate of about 60%. Adding Vertex Pharmaceuticals Incivek or Merck's  Victrelis to the regimen would increase the cure rate to as high as 79% for genotype 1 patients. It's a little dangerous to compare Gilead's data with Vertex's and Merck's data, since they might have enrolled patients with different underlying issues, but it appears sofosbuvir is at least as good, and perhaps better, than the first-generation offerings.


Gilead also presented additional data in patients with genotype 2 or 3. In the trial, dubbed Fission, sofosbuvir plus ribavirin only matched the cure rate of ribavirin and Pegasys, but that's an acceptable result given Pegasys' side effects. Adverse events observed in greater than 10% of patients -- fatigue, headache, nausea, insomnia, and dizziness -- all occurred in patients taking Pegasys.

Gilead has one more phase 3 trial, called Fusion, whose results are anticipated later this quarter, and then Gilead will be able to apply for FDA approval. Unless some safety issue crops up, an approval seems all but certain.

Just don't thnk that sofosbuvir will produce massive sales all on its own. The largest opportunity in the U.S. is in genotype 1 patients, but sales of Incivek continue to fall as patients wait for an all-oral regimen. Remember Gilead only has data combining its drug with Pegasys in that genotype, so don't expect patients to flock to it just yet.

The true test will come when sofosbuvir is tested in combination with GS-5885 and ribavarin. If the all-oral regimen produces cure rates above 80%, it'll have no problem competing with Incivek and Victrelis. Gilead will likely need higher cure rates than that, though, because other competitors are coming up from behind with their own all-oral regimen. AbbVie's  all-oral cocktail produced a 99% cure rate in its phase 2 trial and looked pretty good in patients who had failed to respond to previous treatments.

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The article Piling on the Phase 3 Data originally appeared on Fool.com.

Fool contributor Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends Gilead Sciences and Vertex Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.

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