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 and safety of a new benzodiazepine antagonist , flumazenil , were assessed in a double - blind multicenter study .
### Output Text:
The efficacy and safety of a new <span class="chemical">benzodiazepine</span> antagonist , <span class="chemical">flumazenil</span> , were assessed in a double - blind multicenter study . 