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: A further group of 25 patients under polychemotherapy with IF were treated by conventional prophylactic measures ( raised fluid intake and forced diuresis ) .
### Output Text:
A further group of 25 patients under polychemotherapy with <span class="chemical">IF</span> were treated by conventional prophylactic measures ( raised fluid intake and forced diuresis ) . 