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: Hemoglobin concentrations decrease mainly as a result of ribavirin - induced hemolysis , and this anemia can be problematic in patients with HCV infection , especially those who have comorbid renal or cardiovascular disorders .
### Output Text:
Hemoglobin concentrations decrease mainly as a result of <span class="chemical">ribavirin</span> - induced hemolysis , and this anemia can be problematic in patients with HCV infection , especially those who have comorbid renal or cardiovascular disorders . 