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: Although ribavirin - associated anemia can be reversed by dose reduction or discontinuation , this approach compromises outcomes by significantly decreasing SVR rates .
### Output Text:
Although <span class="chemical">ribavirin</span> - associated anemia can be reversed by dose reduction or discontinuation , this approach compromises outcomes by significantly decreasing SVR rates . 