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: A 1 - year - old female presented with neuroleptic malignant syndrome probably caused by methylphenidate .
### Output Text:
A 1 - year - old female presented with neuroleptic malignant syndrome probably caused by <span class="chemical">methylphenidate</span> . 