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: The efficacy of alprazolam and placebo in panic disorder with agoraphobia , and the side - effect and adverse effect profiles of both drug groups were measured .
### Output Text:
The efficacy of <span class="chemical">alprazolam</span> and placebo in panic disorder with agoraphobia , and the side - effect and adverse effect profiles of both drug groups were measured . 