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: Value of methylprednisolone in prevention of the arthralgia - myalgia syndrome associated with the total dose infusion of iron dextran : a double blind randomized trial .
### Output Text:
Value of <span class="chemical">methylprednisolone</span> in prevention of the arthralgia - myalgia syndrome associated with the total dose infusion of <span class="chemical">iron dextran</span> : a double blind randomized trial . 