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: Nephrotoxicity of cyclosporin A and FK506 : inhibition of calcineurin phosphatase .
### Output Text:
Nephrotoxicity of <span class="chemical">cyclosporin A</span> and <span class="chemical">FK506</span> : inhibition of calcineurin phosphatase . 