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: DESIGN / METHODS : We retrospectively reviewed the medical records of 5 children treated with intravenous ribavirin for documented severe adenovirus disease .
### Output Text:
DESIGN / METHODS : We retrospectively reviewed the medical records of 5 children treated with intravenous <span class="chemical">ribavirin</span> for documented severe adenovirus disease . 