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: CONCLUSIONS : Reduction of ribavirin at hemoglobin level > or = 10 g / dl is suitable in terms of efficacy and side effects .
### Output Text:
CONCLUSIONS : Reduction of <span class="chemical">ribavirin</span> at hemoglobin level > or = 10 g / dl is suitable in terms of efficacy and side effects . 