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: A MEDLINE search ( 1966 - January 2009 ) revealed one in vivo pharmacokinetic study on the interaction between flecainide , a CYP2D6 substrate , and paroxetine , a CYP2D6 inhibitor , as well as 3 case reports of flecainide - induced delirium .
### Output Text:
A MEDLINE search ( 1966 - January 2009 ) revealed one in vivo pharmacokinetic study on the interaction between <span class="chemical">flecainide</span> , a CYP2D6 substrate , and <span class="chemical">paroxetine</span> , a CYP2D6 inhibitor , as well as 3 case reports of <span class="chemical">flecainide</span> - induced delirium . 