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: Bupivacaine , levobupivacaine , or ropivacaine was infused at a rate of 2 mg .
### Output Text:
<span class="chemical">Bupivacaine</span> , <span class="chemical">levobupivacaine</span> , or <span class="chemical">ropivacaine</span> was infused at a rate of 2 mg . 