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: A 63 - year - old male experienced sudden diplopia after 9 weeks of administration of pegylated interferon ( IFN ) alpha - 2b and ribavirin for chronic hepatitis C ( CHC ) .
### Output Text:
A 63 - year - old male experienced sudden diplopia after 9 weeks of administration of <span class="chemical">pegylated interferon ( IFN ) alpha - 2b</span> and <span class="chemical">ribavirin</span> for chronic hepatitis C ( CHC ) . 