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: Paroxetine was discontinued and the dose of flecainide was reduced to 50 mg twice daily .
### Output Text:
<span class="chemical">Paroxetine</span> was discontinued and the dose of <span class="chemical">flecainide</span> was reduced to 50 mg twice daily . 