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: According to the Naranjo probability scale , flecainide was the probable cause of the patient ' s delirium ; the Horn Drug Interaction Probability Scale indicates a possible pharmacokinetic drug interaction between flecainide and paroxetine .
### Output Text:
According to the Naranjo probability scale , <span class="chemical">flecainide</span> was the probable cause of the patient ' s delirium ; the Horn Drug Interaction Probability Scale indicates a possible pharmacokinetic drug interaction between <span class="chemical">flecainide</span> and <span class="chemical">paroxetine</span> . 