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: The protracted infusion schedule for ifosfamide permits convenient outpatient administration without Mesna and reduces the drug cost of clinical usage of this agent by up to 890 per cycle .
### Output Text:
The protracted infusion schedule for <span class="chemical">ifosfamide</span> permits convenient outpatient administration without <span class="chemical">Mesna</span> and reduces the drug cost of clinical usage of this agent by up to 890 per cycle . 