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: This study suggests that for healthy older adults who are not suffering from chronic pain , neurocognitive and pharmacodynamic changes in response to a 10 - mg dose of immediate - release oxycodone are similar to those observed for middle - aged adults .
### Output Text:
This study suggests that for healthy older adults who are not suffering from chronic pain , neurocognitive and pharmacodynamic changes in response to a 10 - mg dose of immediate - release <span class="chemical">oxycodone</span> are similar to those observed for middle - aged adults . 