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: By using a placebo - controlled , two - way factorial design , tolerance to cold - pressor ( CP ) pain was examined , both before and after oral administration of therapeutic doses of common opioid ( hydromorphone 2 mg ) and nonsteroidal anti - inflammatory ( ketorolac 10 mg ) analgesic agents .
### Output Text:
By using a placebo - controlled , two - way factorial design , tolerance to cold - pressor ( CP ) pain was examined , both before and after oral administration of therapeutic doses of common opioid ( <span class="chemical">hydromorphone</span> 2 mg ) and nonsteroidal anti - inflammatory ( <span class="chemical">ketorolac</span> 10 mg ) analgesic agents . 