Every year, the promise of safer and more effective drugs coming to market gives an aging population hope. According to the Phrma organization's website, roughly $49 billion was spent on researching some 2,900 compounds last year alone. The truly amazing part is that we've only touched the tip of the iceberg on what diseases are left to be researched and/or cured. We still have a long way to go with regards to cancer research, and many rare diseases still have largely unmet needs.

Each week for a total of five weeks, I'm going to look at an upcoming drug that has every indication of being not only a revenue blockbuster, but a true life changer. Keep in mind that none of the five drug hopefuls I'll be highlighting are approved by the Food and Drug Administration, so there are plenty of obstacles left to be encountered, including safety data, which could still stand in the way of an ultimate approval.

Last week, I examined Biogen Idec's BG-12 as the first drug hopeful that's set to change people's lives. This week, I want to take a closer look at Gilead Sciences (GILD -0.19%) sofosbuvir.

The name sofosbuvir might not strike a chord with many of you because you may know it better as GS-7977, the experimental hepatitis-C drug acquired by Gilead when it purchased Pharmasset for $11 billion late last year. By all respects, sofosbuvir has performed better than anyone could have hoped for in clinical trials, but that hasn't been the case for Gilead's competitors.

Bristol-Myers Squibb (BMY -0.96%) tried to follow Gilead's lead and buy its way to success by purchasing Inhibitex for $2.5 billion in January. I claimed the purchase a foolish (with a small 'f') idea since Inhibitex's lead hepatitis-C drug was only through early stage clinical trials. True to form, that purchase wound up biting Bristol in the behind in early August when it disclosed that BMS-986094 (the experimental drug acquired with its Inhibitex purchase) caused the death of a patient and complications with multiple others. BMS-986094 was soon permanently shelved, and Bristol wrote down $1.8 billion on its purchase.

Subsequent to Bristol's troubles, Idenix Pharmaceuticals (NASDAQ: IDIX) also ran into trouble of its own. As a maker of nucleotide-based inhibitors, the FDA placed a clinical hold on two of Idenix's hepatitis-C compounds due to potential safety concerns. Idenix has evaluated the safety of its lead compound, IDX-184 and found no evidence of any safety issues, but the clinical holds still remain.

That leads us back to Gilead's sofosbuvir, which was recently combined with GS-5885 and an antiviral ribavirin in a late-stage trial and found to eliminate all detectable levels of the hepatitis C virus in 100% of patients tested four weeks after a 12-week dosing regimen. This isn't the first time Gilead sofosbuvir has proven effective, either. In a combination with Bristol's daclatasvir in mid-stage trials, sofosbuvir eliminated all detectable levels of the disease in in 100% of genotype 1 patients, and 91% in genotype 2 and 3.

On top of sofosbuvir's success in clinical trials, the simple fact that it's an all-oral treatment lends hope that patients will be privy to far fewer side effects than the current standard treatments offered by Vertex Pharmaceuticals (VRTX -1.47%) with Incivek, and Merck (MRK -1.07%) with Victrelis. These current standards are given with interferon, a protein that's given intravenously and known to cause flu-like symptoms for up to 48 weeks during treatment. Sofosbuvir's side effects have shown to be far less severe and abate much more quickly than those associated with interferon.

The market for hepatitis C is huge and could equal as much as $20 billion by 2015, according to analysts at Credit Suisse. According to Barclays analyst Tony Butler, given FDA approval, sofosbuvir could hit peak sales of $3.8 billion, so it's not difficult to understand why so many biotechs want a piece of the hepatitis C pie.

Despite Bristol and Idenix's struggles, there are still plenty of viable competitors including: Abbott Laboratories (ABT 0.64%) which recently reported a 97% success rate in removing detectable levels of the hepatitis C virus with a three drug combination, as well as ribavirin, in mid-stage trials, and Achillion Pharmaceuticals (ACHN) which recently announced proof-of-concept data for its non-nucleotide-based early stage inhibitor, ACH-3102. Yet, it's Gilead's sofosbuvir that has the clear path to approval and the chance to really make a difference in people's lives.

Be sure to check back next week when I unveil the third pipeline drug capable of changing your life for the better.