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 developed weakness , lethargy , and shortness of breath 2 days after starting therapy with omeprazole .
### Output Text:
The patient developed weakness , lethargy , and shortness of breath 2 days after starting therapy with <span class="chemical">omeprazole</span> . 