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 chronic schizophrenic patient was treated with an anticholinergic drug , trihexyphenidyl hydrochloride .
### Output Text:
A chronic schizophrenic patient was treated with an anticholinergic drug , <span class="chemical">trihexyphenidyl hydrochloride</span> . 