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: We conclude that methylphenidate mediated vasculitis should be considered in patients with neurological symptoms and a history of methylphenidate therapy .
### Output Text:
We conclude that <span class="chemical">methylphenidate</span> mediated vasculitis should be considered in patients with neurological symptoms and a history of <span class="chemical">methylphenidate</span> therapy . 