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### Input Text: Propylthiouracil therapy was withdrawn , and she was treated with a 1 - month course of prednisone , which alleviated her symptoms .
### Output Text:
<span class="chemical">Propylthiouracil</span> therapy was withdrawn , and she was treated with a 1 - month course of <span class="chemical">prednisone</span> , which alleviated her symptoms . 