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: Five patients with cancer who developed acute renal failure that followed treatment with ciprofloxacin are described and an additional 15 cases reported in the literature are reviewed .
### Output Text:
Five patients with cancer who developed acute renal failure that followed treatment with <span class="chemical">ciprofloxacin</span> are described and an additional 15 cases reported in the literature are reviewed . 