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: Patients were randomly allocated to either receive or not receive 1 1 fentanyl , while a third group received dexamethasone in addition to fentanyl .
### Output Text:
Patients were randomly allocated to either receive or not receive 1 1 <span class="chemical">fentanyl</span> , while a third group received <span class="chemical">dexamethasone</span> in addition to <span class="chemical">fentanyl</span> . 