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 group assessable for efficacy comprised 122 patients treated with flumazenil and 64 patients given placebo .
### Output Text:
The group assessable for efficacy comprised 122 patients treated with <span class="chemical">flumazenil</span> and 64 patients given placebo . 