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: Azathioprine treatment benefited 19 ( 66 % ) out of 29 patients suffering from severe psoriasis .
### Output Text:
<span class="chemical">Azathioprine</span> treatment benefited 19 ( 66 % ) out of 29 patients suffering from severe psoriasis . 