Complex sentence: COX-2-selective inhibitors react weakly with the COX-3 enzymatic site, because the site is identical to that in COX-1, but they are as good at reducing fever as older NSAIDs.
Split into simpler sentences: COX-2-selective inhibitors react weakly with the COX-3 enzymatic site, because the site is identical to that in COX-1. These are as good at reducing fever as older NSAIDs.