Bristol-Myers Squibb's (NYSE: BMY) latest data on its current hepatitis C drugs explain why the pharma needed to purchase Inihibitex (Nasdaq: INHX). A combination of its drugs -- daclatasvir and asunaprevir -- appears much better at treating patients that didn't respond to their initial treatment than Vertex Pharmaceuticals' (Nasdaq: VRTX) Incivek, but we're a long way off from an all-oral cure for those patients.

An impressive 90% of patients who didn't respond to their first treatment with ribavirin and PEG-interferon alfa -- Roche's Pegasys or Merck's PegIntron -- were essentially virus-free 24 weeks after their second treatment, which included those two drugs plus daclatasvir and asunaprevir. In Vertex's trial, only 32% of those so-called "null responders" achieved the same result when taking Incivek plus the two older drugs. Of course that's still better than just repeating the treatment, which resulted in just 5% of patients responding.

But the goal of hepatitis C drugmakers is to remove PEG-interferon altogether. The drug has some side effects that make it unpleasant to take. In null responders that took just daclatasvir and asunaprevir, only 36% of patients were cleared of the virus. Better than nothing -- Incivek can't even be used on its own -- but a far cry from an all-oral cure for null responders; not to mention that there were only 21 patients in the trial, so the drugs are a ways away from being on the market.

Will adding in Inhibitex's INX-189 help? Let's hope so. Bristol needs something to justify the $2.5 billion purchase. The company also has partnerships to test daclatasvir with Gilead Sciences' (Nasdaq: GILD) PSI-7977 and Johnson & Johnson's (NYSE: JNJ) TMC435, so there are other possibilities to get into whatever cocktail treatment becomes the all-oral standard of care.

Of course, null responders are only a small subset of the hepatitis C patients. And the group should be getting smaller since fewer treatment-naive patients fail their first treatment now that Incivek is available. But treating null responders is the Holy Grail of hepatitis C. Any combination that can treat them shouldn't have any problems treating the easier-to-treat treatment-naive patients.

Follow the hepatitis C drugmakers in their quest for an all-oral treatment by adding them to the Fool's Watchlist service. You can add them all by following this link or add them individually below.

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