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: Further studies are needed to explore tissue bupivacaine levels of propofol in medialipid and adapt these results to clinical practice .
### Output Text:
Further studies are needed to explore tissue <span class="chemical">bupivacaine</span> levels of <span class="chemical">propofol</span> in medialipid and adapt these results to clinical practice . 