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: Cessation of sorafenib and administration of Ca - channel blocker and nitrates ameliorated his symptoms , but relapse occurred after resumption of sorafenib .
### Output Text:
Cessation of <span class="chemical">sorafenib</span> and administration of <span class="chemical">Ca</span> - channel blocker and <span class="chemical">nitrates</span> ameliorated his symptoms , but relapse occurred after resumption of <span class="chemical">sorafenib</span> . 