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: Adverse events considered to be related to levofloxacin administration were reported by 29 patients ( 9 % ) .
### Output Text:
Adverse events considered to be related to <span class="chemical">levofloxacin</span> administration were reported by 29 patients ( 9 % ) . 