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: Factors affecting triamterene nephrolithiasis are discussed and 2 previously reported cases are reviewed .
### Output Text:
Factors affecting <span class="chemical">triamterene</span> nephrolithiasis are discussed and 2 previously reported cases are reviewed . 