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: TDP is a side - effect that has led to withdrawal of several drugs from the market ( e . g . terfenadine and terodiline ) .
### Output Text:
TDP is a side - effect that has led to withdrawal of several drugs from the market ( e . g . <span class="chemical">terfenadine</span> and <span class="chemical">terodiline</span> ) . 