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: In an attempt to obviate the inconvenience of bladder irrigation , we conducted a feasibility trial of uroprophylaxis with mesna , which neutralizes the hepatic metabolite of cyclophosphamide that causes hemorrhagic cystitis .
### Output Text:
In an attempt to obviate the inconvenience of bladder irrigation , we conducted a feasibility trial of uroprophylaxis with <span class="chemical">mesna</span> , which neutralizes the hepatic metabolite of <span class="chemical">cyclophosphamide</span> that causes hemorrhagic cystitis . 