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: CONCLUSIONS : Clinicians are exhorted to pay close attention when initiating levofloxacin therapy in patients taking medications with epileptogenic properties that are CYP1A2 substrates .
### Output Text:
CONCLUSIONS : Clinicians are exhorted to pay close attention when initiating <span class="chemical">levofloxacin</span> therapy in patients taking medications with epileptogenic properties that are CYP1A2 substrates . 