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 firm Idenix Pharmaceuticals (Nasdaq: IDIX) crashed as much as 35% after receiving unfavorable news for its leading experimental drug candidate, IDX184.

So what: Idenix Pharmaceuticals received word from the Food and Drug Administration in a letter today that it was placing a hold on IDX184, a mid-stage treatment for hepatitis C that had shown significant efficacy in recent studies. According to the FDA, the reason for the hold stems from an adverse cardiac event that happened with a competitors' nucleotide polymerase inhibitor. That letter is referring to Bristol-Myers Squibb (NYSE: BMY), which suspended its phase 2 trial of BMS-986094 which it acquired when it purchased Inhibtex for $2.5 billion earlier this year. Gilead Sciences (Nasdaq: GILD), whose GS7977 has been at the forefront of hepatitis C innovation, dropped as well since its drug is also a nucleotide-based inhibitor.

Now what: Don't for one second think this is a reason to run out and buy Achillion Pharmaceuticals (Nasdaq: ACHN) since it has a non-nucleotide-based treatment, because it's not! There's very little reason here to believe that Gilead Sciences will have any long-term effect from Idenix's bad news; I hold this as even more evidence that Gilead has the clear path to be the first non-interferon-based hepatitis C treatment to be approved by the FDA. Until that time, the hepatitis C market is Vertex Pharmaceuticals' (Nasdaq: VRTX) to lose and Incivek will remain the premier treatment. Idenix clearly has a lot of hurdles to overcome and there just may not be much of the hepatitis C pie left by the time it works out all of its kinks.

Craving more input? Start by adding Idenix Pharmaceuticals to your free and personalized watchlist so you can keep up on the latest news with the company.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.