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: METHODS : Twenty renal transplant recipients were switched to fixed dose rapamycin ( RAPA ) ( 5 mg / day ) 0 to 204 months posttransplant .
### Output Text:
METHODS : Twenty renal transplant recipients were switched to fixed dose <span class="chemical">rapamycin</span> ( <span class="chemical">RAPA</span> ) ( 5 mg / day ) 0 to 204 months posttransplant . 