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 she discontinued the omeprazole , her hemoglobin and hematocrit gradually returned to normal .
### Output Text:
After she discontinued the <span class="chemical">omeprazole</span> , her hemoglobin and hematocrit gradually returned to normal . 