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: Following short exposure to oral prednisone , both boys developed lethargy , increasing somnolence , polydipsia , polyphagia , and polyuria .
### Output Text:
Following short exposure to oral <span class="chemical">prednisone</span> , both boys developed lethargy , increasing somnolence , polydipsia , polyphagia , and polyuria . 