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: Cerebral vasculitis associated with amphetamine abuse is well documented , and in rare cases ischaemic stroke has been reported after methylphenidate intake in children .
### Output Text:
Cerebral vasculitis associated with amphetamine abuse is well documented , and in rare cases ischaemic stroke has been reported after <span class="chemical">methylphenidate</span> intake in children . 