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16. Pfizer
Fortune 500 rank: 47
2007 profit: $8.14 billion

If 2007 is any indication, Pfizer has a tough road ahead. Profit fell a thumping 58% on sales that were down 8%, dropping the drugmaker 10 spots from last year's most-profitable list.

Pfizer lost several important patents during the year, including one for Norvasc, a blood pressure drug with nearly $5 billion in 2006 sales.

And it doesn't get easier. Around 2010, the drugmaker loses its patent on Lipitor, the successful anti-cholesterol drug.

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Last updated April 24 2008: 11:07 AM ET