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: RAPA levels were high ( > 15 ng / ml ) in 7 of 13 ( 54 % ) patients .
### Output Text:
<span class="chemical">RAPA</span> levels were high ( > 15 ng / ml ) in 7 of 13 ( 54 % ) patients . 