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: BACKGROUND : Pre - treatment with lipid emulsions has been shown to increase lethal doses of bupivacaine , and the lipid content of propofol may alleviate bupivacaine - induced cardiotoxicity .
### Output Text:
BACKGROUND : Pre - treatment with lipid emulsions has been shown to increase lethal doses of <span class="chemical">bupivacaine</span> , and the lipid content of <span class="chemical">propofol</span> may alleviate <span class="chemical">bupivacaine</span> - induced cardiotoxicity . 