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: After that , these 37 patients were reduced one tablet of ribavirin ( 200 mg ) per day .
### Output Text:
After that , these 37 patients were reduced one tablet of <span class="chemical">ribavirin</span> ( 200 mg ) per day . 