Five years ago, ViroPharma (NASDAQ: VPHM) had everything going for it. Sales of the company's lead drug, Vancocin -- an FDA-approved treatment for Clostridium difficile and other gastrointestinal infections -- were roaring higher. Maribavir -- an experimental anti-cytomegalovirus, or CMV, drug for bone marrow and liver transplant patients -- was showing plenty of promise in trials.

However, that unicorn has long since flown away.

ViroPharma's Vancocin had been under pressure from generic competition since 2008, using a citizens petition with 18 separate supplements -- essentially everything in the book -- in an effort to block Actavis (NYSE:AGN) (previously Watson Pharmaceuticals) and Akorn (NASDAQ:AKRX) from bringing generic Vancocin, known as vancomycin, to market. Last year, ViroPharma lost that bid when the Food and Drug Administration approved three generic forms of vancomycin (including Actavis and Akorn's generics). Further, a federal judge dismissed ViroPharma's lawsuit against the FDA earlier this year over allowing generic forms of Vancocin to hit the market. 

Before this, in 2009, maribavir failed to meet its primary and secondary endpoint in late-stage trials, which came as a shock to many. Despite strong mid-stage results, maribavir delivered a non-statistically significant CMV disease incidence rate of 4.4% after 180 days compared to an incidence rate of 4.8% for the placebo.

At that moment, it appeared that maribavir would be just another experimental treatment ready to be put out to pasture; but that's not the case anymore. In fact, it appears that ViroPharma just may have successfully brought maribavir back from the dead!

Just yesterday, ViroPharma announced that maribavir had been granted orphan drug status in Europe for the treatment of CMV disease in patients with impaired cell-mediated immunity. ViroPharma is pulling off its previous trial data, which was based on a 100mg dose, and bumping up the testing dosage in mid-stage trials to 400mg, 800mg, and 1,200mg. Ultimately, it may not have been that maribavir was ineffective in 2009, but simply that the dosing was insufficient to beat back the CMV disease.

Possibly working in ViroPharma's favor is the fact that Roche's (OTC:RHHBY) COBAS AmpliPrep/COBAS Taqman CMV Test was approved in 2012 by the FDA to gauge the progress of CMV disease in solid organ transplant patients. CMV has no cure, which makes the need for effective CMV medications critical and the accuracy of progression testing like this crucial if maribavir is going to be successful. 

Initial estimates by ViroPharma at its 2012 investors day with analysts are that Maribavir represents a $300 million global opportunity. The company is also running dosing trials once again in the U.S. for CMV disease in similar fashion to Europe.

In addition to residual Vancocin sales, hereditary angioedema drug Cinryze -- which ViroPharma acquired when it purchased Lev Pharmaceuticals in 2008 -- is on fire, with sales growing 44% in the first quarter and the company expecting up to $400 million in revenue this year from the drug at the top end of its forecast.

ViroPharma is certainly still dealing with the stigma of losing its previous workhorse in Vancocin, but its future is again looking bright. I figured there was an outside chance that the 2009 data from maribavir was bound to induce ViroPharma to dig deeper, especially with CMV disease having no cure, and it appears my speculation was correct. I would keep a very close eye on ViroPharma moving forward as it appears to have the right tools and the budding pipeline to really surprise Wall Street and investors.

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.