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: Comparative cognitive and subjective side effects of immediate - release oxycodone in healthy middle - aged and older adults .
### Output Text:
Comparative cognitive and subjective side effects of immediate - release <span class="chemical">oxycodone</span> in healthy middle - aged and older adults . 