Merck (NYSE: MRK) got off the starting line first, but this is a marathon -- and I doubt its lead on Vertex Pharmaceuticals (Nasdaq: VRTX) will amount to much.

The Food and Drug Administration approved Merck's hepatitis C drug Victrelis on Friday, which could give it a 10-day head start over Vertex's Incivek. The FDA's goal is to make a decision about Incivek by May 23, although it's not bound to that date.

Even if the agency takes a few extra days or even a week, it won't make much difference. Hepatitis C is a life-threatening illness, but it isn't an immediate life-threatening illness. The virus causes liver damage, but it happens rather slowly. Patients can live with the disease for years without any major issues. Doctors aren't going to rush out and treat the estimated 3.2 million Americans with the disease in the next seven days.

A long delay, like the FDA requiring more clinical trials for Incivek, would be a major problem -- not that anyone is expecting that. Even under that worst-case scenario, there would still be patients available when it was approved. At least, Gilead Sciences (Nasdaq: GILD), Bristol-Myers Squibb (NYSE: BMY), and many others coming up from behind certainly hope so. For these firms, gaining additional time might allow them to catch up with potentially similar drugs under development. However, don't necessarily count on this to be the case.

While the slight lead may not amount to anything, Merck does have a marketing advantage because the drugmaker already sells Pegintron, one of the current treatments to which Victrelis and Incivek will be added. Its sales force could hit the ground running more quickly than that of Vertex. Experience with European hepatologists will also benefit Merck while it's competing with Johnson & Johnson (NYSE: JNJ), which will market Incivek in Europe for Vertex.

But Incivek has generally put out better data than Victrelis, so it's not clear how much Merck's experience will really benefit sales.

We should find out starting in seven days or so.

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