The new class of drugs, called Cyclooxygenase-2 or Cox-2 inhibitors, are no better at easing swelling or numbing hurt.

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The only difference between the two types of cyclooxygenase is a small pocket that protrudes, like the thumb of a glove, from the main binding site.

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Drugs such as Vioxx and Pfizer 's (nyse: PFE - news - people ) Celebrex inhibit cyclooxygenase-2, or Cox-2, an enzyme involved in inflammation.

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Needleman's theory was that one could spare the stomach by selectively blocking the enzyme responsible for inflammation, COX-2 (cyclooxygenase-2), while avoiding the one involved in maintaining the stomach lining, COX-1.

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Cox-2 inhibitors, developed with much hype in the mid-1990s, block an enzyme called cyclooxygenase-2, in so doing shutting off a wide-reaching cascade of biochemical signals that take the form of fats called prostaglandins.

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