In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In the present study , we describe the proinflammatory effects of bupivacaine on local prostaglandin E2 ( PGE2 ) production and cyclooxygenase ( COX ) gene expression that increases postoperative pain in human subjects .
### Output Text:
In the present study , we describe the proinflammatory effects of <span class="chemical">bupivacaine</span> on local <span class="chemical">prostaglandin E2</span> ( <span class="chemical">PGE2</span> ) production and cyclooxygenase ( COX ) gene expression that increases postoperative pain in human subjects . 