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: METHODS : Subjects ( n = 114 ) undergoing extraction of impacted third molars received either 2 % lidocaine or 0 . 5 % bupivacaine before surgery and either rofecoxib 50 mg or placebo orally 90 min before surgery and for the following 48 h .
### Output Text:
METHODS : Subjects ( n = 114 ) undergoing extraction of impacted third molars received either 2 % <span class="chemical">lidocaine</span> or 0 . 5 % <span class="chemical">bupivacaine</span> before surgery and either <span class="chemical">rofecoxib</span> 50 mg or placebo orally 90 min before surgery and for the following 48 h . 