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: PURPOSE : To evaluate the efficacy and safety of levofloxacin ( 500 mg orally once daily for 10 to 14 days ) in treating adult outpatients with acute bacterial sinusitis .
### Output Text:
PURPOSE : To evaluate the efficacy and safety of <span class="chemical">levofloxacin</span> ( 500 mg orally once daily for 10 to 14 days ) in treating adult outpatients with acute bacterial sinusitis . 