The drug: Bapineuzumab
The disease: Alzheimer's
The developers: J&J, Pfizer and Elan
Peak projections: $5 billion-$10 billion

Once estimated as a potential mega-earner with more than $10 billion in annual sales potential, things changed in 2008 when a brain swelling condition spotted in patients taking the drug raised red flags. Recently, however, the FDA eased guidelines on the Alzheimer's patients who could be recruited for studies of drugs that aim to reduce levels of amyloid in the brains of patients.

Now Elan, which was once pilloried for hyping the potential of the drug, is counting on its stake in future sales revenues as a way to leverage its way out of the red ink it's been seeing every year. J&J clearly loved the drug's potential, snagging a big stake in the program with its billion-dollar deal in 2009. In the spring of 2010, investigators for J&J opted to broaden the program into one of the largest Alzheimer's programs ever mounted. Analysts fretted as the scientists pushed back delivery on pivotal data.

They've had to learn patience. Elan and Wyeth originally set out to obtain pivotal data in 2007.

The potential for problems are enormous. Not the least of the developers' worries is that investigators are operating on assumptions: In this case that this biomarker for Alzheimer's is also the best drug target. There's no conclusive proof that's the case.

UBS analyst Guillaume van Renterghem once estimated top potential worldwide sales at $8 billion, but with so many variables, it's hard to tell.

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