WebMD Medical News
Daniel J. DeNoon
Laura J. Martin, MD
Aug. 9, 2010 -- Adding Merck's boceprevir to standard hepatitis C therapy increases the viral cure rate up to 75% -- a success rate similar to that of Vertex's telaprevir.
Standard hepatitis C treatment results in a "cure" less than half the time. It combines alpha interferon with ribavirin, a drug with general antiviral effects. In contrast, boceprevir and telaprevir directly attack the hepatitis C virus (HCV).
Boceprevir and telaprevir each inhibit the HCV protease molecule. Like HIV protease inhibitors, these HCV protease inhibitors are extremely effective at suppressing the virus they target.
Unfortunately, there's another similarity. Like the AIDS virus, the hepatitis virus quickly develops resistance to protease inhibitors. Neither boceprevir nor telaprevir can be given alone -- each must be added to standard combination treatment with alpha interferon and ribavirin.
That standard combination causes a lot of hard-to-tolerate side effects. Both boceprevir and telaprevir add to the side effect burden. Very preliminary evidence suggests that boceprevir may be somewhat easier to take.
Nevertheless, the boceprevir findings are very good news for people with hepatitis C infection. They show the drug greatly increases the odds that treatment will result in a cure -- that is, in HCV dropping to undetectable levels. Patients who achieve such a "sustained viral response" (SVR) or "viral cure" usually don't see the virus come back to harmful levels.
The boceprevir studies tested the drug in patients with genotype 1 HCV infection. Genotype 1 is the most common HCV strain in the U.S. and is generally considered the most resistant to treatment.
In a phase III clinical trial reported by Merck, among never-before-treated patients:
In another phase III clinical trial reported by Merck, among patients for whom previous treatment failed:
In a smaller phase II studies of boceprevir, Paul Y. Kwo, MD, of Indiana University, and colleagues found that 75% of patients achieved an SVR by starting standard treatment four weeks before adding the new drug to the combination.
The hope is that by suppressing the virus before starting boceprevir, resistance to the new drug could be delayed or avoided. It seemed to work: Patients on this schedule were five times more likely to have an SVR than those on standard treatment.
It's not clear from the phase III data released by Merck whether the strategy is a success. More detailed results from these late-stage trials will be announced this fall at a meeting of liver disease specialists.
The new studies are not all good news. It had been hoped that boceprevir would let patients reduce the dose of hard-to-tolerate ribavirin, but the full dose seems necessary for most patients.
And even with the improved success rate, at least one in four patients won't be cured by the new three-drug combination. In an editorial accompanying the Kwo study, Laura Milazzo and Spinello Antinori of the University of Milan, Italy, note that new drugs -- in new combinations -- will be needed.
Merck says it will file for FDA approval of boceprevir by the end of this year.
The Kwo study, and the Milazzo/Antinori editorial, appear in the Aug. 9 online issue of The Lancet.
SOURCES:News release, Merck.Kwo, P.Y. The Lancet, published online Aug. 9, 2010.Milazzo, L. and Antinori, S. The Lancet, published online Aug. 9, 2010.News release, Indiana University.
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