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 this regimen produces sustained virologic responses ( SVRs ) in approximately 50 % of patients , it can be associated with a potentially dose - limiting hemolytic anemia .
### Output Text:
Although this regimen produces sustained virologic responses ( SVRs ) in approximately 50 % of patients , it can be associated with a potentially dose - limiting hemolytic anemia . 