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: All the complaints disappeared after stopping pegylated interferon alpha - 2b and reappeared after restarting it .
### Output Text:
All the complaints disappeared after stopping <span class="chemical">pegylated interferon alpha - 2b</span> and reappeared after restarting it . 