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: CONCLUSION : The results of this study indicate that levofloxacin 500 mg once daily is an effective and safe treatment for acute bacterial sinusitis .
### Output Text:
CONCLUSION : The results of this study indicate that <span class="chemical">levofloxacin</span> 500 mg once daily is an effective and safe treatment for acute bacterial sinusitis . 