Last week, Rule Breakers pick InterMune (NASDAQ:ITMN) announced gloomy first-quarter results that sent shares falling more than 4%. But investors should know that InterMune's future is looking brighter than ever despite a setback with its only marketed drug last quarter.

In March, InterMune said its only revenue-producing drug, Actimmune, failed in a phase 3 study for treating idiopathic pulmonary fibrosis. Though the company was getting nearly all of its revenue from this off-label treatment, the drug has been approved for treating two other diseases. InterMune had given guidance of $70 million to $90 million in Actimmune sales for the year, but rescinded this after the trial results came out.

In the first quarter, Actimmune sales were down nearly 20% to $20 million, but this was because study results came out so late in the quarter. Sales should fall much further in the next quarters. Because nearly all Actimmune sales are as a treatment for idiopathic pulmonary fibrosis, or IPF, it should come as no surprise that revenue from the drug has declined and will decline further.

InterMune's work on IPF isn't done yet, because it's still running a phase 3 study with its exciting pirfenidone compound, with top-line results pushed up several months -- expected by the end of 2008 -- because of quicker enrollment for the trial. 

While no data about its effectiveness is out yet for InterMune's hepatitis C protease inhibitor, ITMN-191, InterMune's management keeps tantalizing us with little tidbits about the drug during the quarterly conference calls. The latest is about its potential for once-a-day dosing or at least an improved twice-a-day dosing versus the three times a day for Vertex's (NASDAQ:VRTX) HCV treatment, telaprevir. Telaprevir showed strong trial results in a phase 2 study last month, which bodes well for the protease inhibitor class of compounds in treating HCV.

The first ITMN-191 results are expected to be out by the end of the year, and with the pirfenidone phase 3 study enrolling patients so quickly, the future looks bright for InterMune despite the hit it's expected to take from the lost Actimmune sales.

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Fool contributor Brian Lawler owns shares of InterMune but no other company mentioned in this article. The Fool has a disclosure policy.