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 , specific immunophilin - drug - calcineurin complexes formed only in the presence of CsA and FK506 , but not rapamycin .
### Output Text:
Finally , specific immunophilin - drug - calcineurin complexes formed only in the presence of <span class="chemical">CsA</span> and <span class="chemical">FK506</span> , but not <span class="chemical">rapamycin</span> . 