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: Cases reported by the FDA showed clarithromycin and ciprofloxacin to be the most frequently associated with the development of mania .
### Output Text:
Cases reported by the FDA showed <span class="chemical">clarithromycin</span> and <span class="chemical">ciprofloxacin</span> to be the most frequently associated with the development of mania . 