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: Viramidine , a liver - targeting prodrug of ribavirin , has the potential to maintain the virologic efficacy of ribavirin while decreasing the risk of hemolytic anemia in patients with chronic hepatitis C .
### Output Text:
<span class="chemical">Viramidine</span> , a liver - targeting prodrug of <span class="chemical">ribavirin</span> , has the potential to maintain the virologic efficacy of <span class="chemical">ribavirin</span> while decreasing the risk of hemolytic anemia in patients with chronic hepatitis C . 