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: OBJECTIVE : Dexmedetomidine and propofol are commonly used sedatives in neurocritical care as they allow for frequent neurologic examinations .
### Output Text:
OBJECTIVE : <span class="chemical">Dexmedetomidine</span> and <span class="chemical">propofol</span> are commonly used sedatives in neurocritical care as they allow for frequent neurologic examinations . 