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: Since bupivacaine and epinephrine may both precipitate dysrhythmias , circulating bupivacaine during regional anesthesia could potentiate dysrhythmogenic effects of epinephrine .
### Output Text:
Since <span class="chemical">bupivacaine</span> and <span class="chemical">epinephrine</span> may both precipitate dysrhythmias , circulating <span class="chemical">bupivacaine</span> during regional anesthesia could potentiate dysrhythmogenic effects of <span class="chemical">epinephrine</span> . 