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: This neuropathy was gradually resolving ; however , after the patient received allogeneic bone marrow transplantation , the symptoms worsened , with the development of graft - versus - host disease , and the symptoms subsequently responded to methylprednisolone .
### Output Text:
This neuropathy was gradually resolving ; however , after the patient received allogeneic bone marrow transplantation , the symptoms worsened , with the development of graft - versus - host disease , and the symptoms subsequently responded to <span class="chemical">methylprednisolone</span> . 