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: DISCUSSION : Flecainide and pharmacologically similar agents that interact with sodium channels may cause delirium in susceptible patients .
### Output Text:
DISCUSSION : <span class="chemical">Flecainide</span> and pharmacologically similar agents that interact with <span class="chemical">sodium</span> channels may cause delirium in susceptible patients . 