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: The patient ' s ophthalmological symptoms improved rapidly 3 weeks after discontinuation of pegylated IFN alpha - 2b and ribavirin .
### Output Text:
The patient ' s ophthalmological symptoms improved rapidly 3 weeks after discontinuation of <span class="chemical">pegylated IFN alpha - 2b</span> and <span class="chemical">ribavirin</span> . 