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: PERSPECTIVE : Study findings indicate that the metabolism , neurocognitive effects , and physical side effects of oral oxycodone are similar for healthy middle - aged and older adults .
### Output Text:
PERSPECTIVE : Study findings indicate that the metabolism , neurocognitive effects , and physical side effects of oral <span class="chemical">oxycodone</span> are similar for healthy middle - aged and older adults . 