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: The reduction of cyclosporine - or tacrolimus trough levels and the administration of calcium channel blockers led to relief of pain .
### Output Text:
The reduction of <span class="chemical">cyclosporine</span> - or <span class="chemical">tacrolimus</span> trough levels and the administration of <span class="chemical">calcium</span> channel blockers led to relief of pain . 