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: Also , the multichannel blockers Amiodarone , Paroxetine , Terfenadine and Citalopram prolonged FPDc in a concentration dependent manner .
### Output Text:
Also , the multichannel blockers <span class="chemical">Amiodarone</span> , <span class="chemical">Paroxetine</span> , <span class="chemical">Terfenadine</span> and <span class="chemical">Citalopram</span> prolonged FPDc in a concentration dependent manner . 