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: Drug - drug interactions related to the inhibition of CYP1A2 by levofloxacin are likely involved in the clinical outcome of these cases .
### Output Text:
Drug - drug interactions related to the inhibition of CYP1A2 by <span class="chemical">levofloxacin</span> are likely involved in the clinical outcome of these cases . 