Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of hepatitis-C-focused biotechnology company Achillion Pharmaceuticals dropped as much as 12% following the release of interim results for a phase 2a trial with its lead drug candidate, ACH-3102.

So what: The interim data released today was based on just eight patients with genotype 1b. Based on the data, ACH-3102, which is given with ribavirin, has been well tolerated in all patients. Three of the patients have completed 12 weeks of treatment, with five others having completed four weeks. The two primary endpoints, in addition to safety goals, are a rapid virologic response, or RVR, as well as an end of treatment response, or ETR. All three patients who have completed the 12 week treatment demonstrated the expected ETR; however, only four of five patients after four weeks met the RVR endpoint.


Now what: Given that Gilead Sciences'  sofosbuvir has been nearly perfect by itself and in combination with other drugs --including its own GS-5885 and Bristol-Myers Squibb's daclatasvir -- Achillion's ACH-3102 practically needs to have perfect marks across the board to get investors excited. Today's data is incomplete and just a snippet of what to expect, but even that one patient of five not to meet the RVR endpoint is enough to concern investors. I remain steadfast in my opinion that Gilead is the way to play the hepatitis-C sector and all other competitors are merely second fiddle at best.

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The article Why Achillion Pharmaceuticals' Shares Soured originally appeared on Fool.com.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong. Motley Fool newsletter services have recommended buying shares of Gilead Sciences. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.

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