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: Finally , the IKr blockers , Terfenadine and Citalopram , which are reported to cause Torsade de Pointes ( TdP ) in clinical practice , produced early afterdepolarization ( EAD ) .
### Output Text:
Finally , the IKr blockers , <span class="chemical">Terfenadine</span> and <span class="chemical">Citalopram</span> , which are reported to cause Torsade de Pointes ( TdP ) in clinical practice , produced early afterdepolarization ( EAD ) . 