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: Torsade de pointes can be treated when recognized early , possibly without discontinuation of pentamidine .
### Output Text:
Torsade de pointes can be treated when recognized early , possibly without discontinuation of <span class="chemical">pentamidine</span> . 