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: An 84 - year - old male received oral pilsicainide , a pure sodium channel blocker with slow recovery kinetics , to convert his paroxysmal atrial fibrillation to a sinus rhythm ; the patient developed sudden cardiac death two days later .
### Output Text:
An 84 - year - old male received oral <span class="chemical">pilsicainide</span> , a pure <span class="chemical">sodium</span> channel blocker with slow recovery kinetics , to convert his paroxysmal atrial fibrillation to a sinus rhythm ; the patient developed sudden cardiac death two days later . 