Most Valuable Drugs
Large pharmaceutical companies differ in how diversified their revenue stream is. This chart shows the most valuable drug for 11 of the 12 largest pharmaceutical companies and what percentage of their pharmaceutical revenue it represents.
As we can see, Bristol Myers Squibb and Abbott Laboratories are the outliers, heavily dependent on a single drug. Also note that Pfizer is vulnerable here as Lipitor lost patent protection in November of 2011, so its revenue is sure to fall in 2012 and beyond.
All data comes from publicly available SEC and other governmental filings. I was unable to find GlaxoSmithKline's pharmaceutical revenue broken out by individual drug, so they are not listed here.