Vertex Pharmaceuticals' (Nasdaq: VRTX) hepatitis C drug telaprevir clearly works. In trials with treatment-naive patients, telaprevir has been the clear winner over Merck's (NYSE: MRK) boceprevir, but the final phase 3 test -- in patients that had failed previous treatments -- was just as important.

There's big money to be made in the treatment-experienced patients for the second-generation drugs. The current options from Roche and Merck only cure about 50% of the patients treated with them, so there are a lot of patients sitting around with virus running through their blood stream waiting for next-generation drugs to become available.

In a clinical trial dubbed REALIZE, the drug was able to knock down viral levels in hepatitis C patients to undetectable levels -- essentially a cure -- in 65% of patients who had failed a previous therapy. Repeating the current standard of care -- the control group -- resulted in a 17% cure rate in these hard-to-treat patients.

On the surface, that 65% cure rate looks comparable to the 66% of the treatment-experienced patients who were cured on boceprevir, but the control group patients in Merck's trial were cured 21% of the time, meaning that telaprevir apparently did a better job. Vertex was nice enough to break down the cure rates between the treatment classes (those who had relapsed vs. those who had not responded vs. those who had partially responded) in its press release, but Merck didn't. So, we'll have to wait until Merck presents more data before we can get an accurate picture of how the two drugs match up in treatment-experienced patients.

Maybe the best news for Vertex and marketing partner Johnson & Johnson (NYSE: JNJ) was the lack of news about side effects. The drug has worked so well in the earlier trials that a new side effect was likely the only thing that could have kept the drug off the market. Just yesterday, Idenix Pharmaceuticals (Nasdaq: IDIX) halted clinical trials of two of its hepatitis C compounds because of side effects. Other treatments -- ViroPharma's (Nasdaq: VPHM) HCV-796 and InterMune's (Nasdaq: ITMN) danoprevir just to name two -- have run into issues. Telaprevir causes a rash in some patients, but it seems to be a minor enough side effect that it won't derail the drug.

With the risk nearly gone, Vertex's investors can sit back and wait for the biotech to start bringing in the revenue.

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