When Vertex Pharmaceuticals (Nasdaq: VRTX) said back in October that the low dose of VX-222 combined with telaprevir was being stopped because of viral breakthrough, I told subscribers of Motley Fool Rule Breakers not to worry. "All drugs fail to work at some suboptimal dose," I wrote.

Now I'm a little worried.

The higher dose of VX-222 combined with telaprevir also failed to rid patients of their hepatitis C. Like the lower dose, this arm of the study was discontinued because of viral breakthrough -- the drug lowers the viral count, but then the virus finds a way around the drug and starts multiplying again.

Vertex is still testing the drug as part of a four-drug combination with telaprevir and Roche's Pegasys and Copegus at two different doses of VX-222. But the four-drug regimen isn't nearly as convenient as a two-drug regimen, especially given the annoying side effects of Pegasys and the fact that it has to be injected.

Now that the next-generation oral hepatitis C drugs -- telaprevir and Merck's (NYSE: MRK) boceprevir -- are on their way to the market, companies want to develop all-oral treatment regimens to avoid Pegasys and its counterpart, PegIntron, which is sold by Merck.

Gilead Sciences (Nasdaq: GILD) has seven oral hepatitis C drugs in development. Roche is developing oral drugs as well; it recently took danoprevir off InterMune's (Nasdaq: ITMN) hands. The easiest way for Vertex to ensure that telaprevir is part of the all-oral treatment regimen is to develop a combination itself.

Vertex is also testing VX-222 in combination with telaprevir and Copegus. The three-drug all-oral combination would avoid Pegasys, but it's unclear whether adding Copegus will be enough to push the efficacy high enough. If it does work, Copegus is available as a generic, so Vertex could theoretically design a combined pill that contained all three drugs.

We'll know soon enough whether VX-222 has any antiviral activity. Interim data from both of the four-drug treatment arms are expected in the first quarter of next year. Investors will just have to be a little worried until then.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.