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: Although the patient ' s renal function was not highly impaired and the dose of pilsicainide was low , the plasma concentration of pilsicainide may have been high , which can produce torsades de pointes in the octogenarian .
### Output Text:
Although the patient ' s renal function was not highly impaired and the dose of <span class="chemical">pilsicainide</span> was low , the plasma concentration of <span class="chemical">pilsicainide</span> may have been high , which can produce torsades de pointes in the octogenarian . 