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: CONCLUSIONS : Supratherapeutic flecainide plasma concentrations may cause delirium .
### Output Text:
CONCLUSIONS : Supratherapeutic <span class="chemical">flecainide</span> plasma concentrations may cause delirium . 