) -- A combination regimen of oral hepatitis C drugs developed by


(ABT) - Get Report

achieved near-perfect cure rates in patients new to treatment. Cure rates were almost as strong in patients who failed previous therapy, making them among the hardest to treat.

With cure rates of 99% following a 12-week regimen of oral drugs, Abbott stamps itself as a strong challenger to

Gilead Sciences

(GILD) - Get Report

in the rapidly evolving race to develop potent, interferon-free regimens for hepatitis C.

Abbott shares rose more than 3% to $71.60 following the release of the hepatitis C data.

The new Abbott data announced Monday come from a large, phase II study known as "AVIATOR" that was designed to assess the efficacy and safety of various combinations of oral hepatitis drugs in treatment-naive patients as well as hard-to-treat "null" responders.

The Abbott drugs studied in AVIATOR were ABT-450, a protease inhibitor that requires blood-boosting with ritonavir; ABT-267, a NS5A inhibitor; and ABT-333, a "non-nuc" polymerase inhibitor. Ribavirin, a current backbone in hepatitis C treatment, was also included in some but not all of the combination regimens.

A 12-week regimen consisting of all three Abbott drugs plus ribavirin demonstrated "observed" SVR12 rates of 99% (76/77) in treatment-naive patients and 93% (38/41) in null responders.

SVR12 is the scientific jargon for a cure and measures the percent of patients who have undetectable hepatitis C virus in their system 12 weeks after treatment ends.

The "observed" SVR12 results omit two treatment-naive patients and four null responder patients with either missing data or inadequate follow-up. If those patients were included and all failed to achieve an SVR12 cure -- a worst-case scenario -- the treatment-naive and null responder cure rates would drop to 96% and 84%, respectively.

Sixty-six percent of the patients enrolled in the Abbott study has genotype 1A virus, considered more resistant to treatment than genotype 1b. Similarly, 70% of patients had unfavorable "non-CC" genetics.

The AVIATOR study also treated patients with regimens consisting of two (not three) Abbott drugs with ribavirin, some with shortened treatment to eight weeks (not 12 weeks.) SVR12 cure rates in these various arms of the study ranged from 89-92%, Abbott announced.

More detailed data from the AVIATOR study will be presented in November at the American Association for the Study of Liver Disease (AASLD) annual meeting.

To put the Abbott results released Monday in perspective, consider that hepatitis C cure rates for treatment-naive patients have risen from approximately 45% with long-acting interferon and ribavirin to 75-80% when

Vertex Pharmaceuticals'

(VRTX) - Get Report

Incivek is added to interferon/ribavirin.

The Abbott data in null responders is even more dramatic given that only about 5% of these hard-to-treat patients were cured by interferon and ribavirin alone. Adding Vertex's Incivek increased null responder cure rates to about 30%.

Among more recent all-oral hepatitis C regimens currently being studied, a combination of

Bristol-Myers Squibb's

(BMY) - Get Report

daclatasvir plus Gilead's GS-7997 dosed for 24 weeks achieved an

SVR4 rate of 100%

in genotype 1, treatment-naive patients. Bristol may present updated SVR12 cure rates from this very promising regimen at the AASLD meeting, but future studies are not planned because

Gilead refused to cooperate


Instead, Gilead is pushing ahead with its own, all-oral regimen consisting of 12 weeks of GS-7977, GS-5885 (a NS5A inhibitor just like Bristol's daclatasvir) with and without ribavirin. Early SVR4 cure data in treatment-naive patients may be announced today but certainly at the AASLD meeting.

Gilead has already starting enrolling patients in phase III studies that could see its hepatitis C regimens approved late next year. Abbott's

phase III studies have not opened for patient enrollment

, which means approval may not come until late 2014.

Gilead's other advantage is convenience. The GS-7977/GS-5885 regimen is being co-formulated into a single, once-daily pill. Abbott's combination regimen consists of pills that must be taken either once a day or twice a day, making compliance more complicated.

-- Reported by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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