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: Because toxicity may occur when flecainide is prescribed with paroxetine and other potent CYP2D6 inhibitors , flecainide plasma concentrations should be monitored closely with commencement of CYP2D6 inhibitors .
### Output Text:
Because toxicity may occur when <span class="chemical">flecainide</span> is prescribed with <span class="chemical">paroxetine</span> and other potent CYP2D6 inhibitors , <span class="chemical">flecainide</span> plasma concentrations should be monitored closely with commencement of CYP2D6 inhibitors . 