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: BACKGROUND : We clinically and pathologically analyzed renal allografts from 1 9 renal transplant patients treated with tacrolimus ( FK506 ) for more than 1 year .
### Output Text:
BACKGROUND : We clinically and pathologically analyzed renal allografts from 1 9 renal transplant patients treated with <span class="chemical">tacrolimus</span> ( <span class="chemical">FK506</span> ) for more than 1 year . 