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 protective effect of oral administration of the thiol compound sodium 2 - mercaptoethane sulphonate ( MESNA ) against urothelial toxicity induced by ifosfamide ( IF ) was tested in a group of 45 patients with inoperable lung cancer under treatment with IF ( 2250 mg / m2 on days 2 - 5 ) as part of a polychemotherapy regimen repeated in a 4 - week cycle .
### Output Text:
The protective effect of oral administration of the <span class="chemical">thiol</span> compound <span class="chemical">sodium 2 - mercaptoethane sulphonate</span> ( <span class="chemical">MESNA</span> ) against urothelial toxicity induced by <span class="chemical">ifosfamide</span> ( <span class="chemical">IF</span> ) was tested in a group of 45 patients with inoperable lung cancer under treatment with <span class="chemical">IF</span> ( 2250 mg / m2 on days 2 - 5 ) as part of a polychemotherapy regimen repeated in a 4 - week cycle . 