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: Progressive improvement occurred in 7 cases after commencement of prednisolone and methotrexate , and in one case spontaneously .
### Output Text:
Progressive improvement occurred in 7 cases after commencement of <span class="chemical">prednisolone</span> and <span class="chemical">methotrexate</span> , and in one case spontaneously . 