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: METHOD : In London and Toronto 154 patients who met DSM - III criteria for panic disorder with agoraphobia were randomised to alprazolam or placebo .
### Output Text:
METHOD : In London and Toronto 154 patients who met DSM - III criteria for panic disorder with agoraphobia were randomised to <span class="chemical">alprazolam</span> or placebo . 