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: OBJECTIVES : The objectives of this study were to examine the relationship between APOE epsilon4 and subjective effects of trihexyphenidyl on measures reflecting sedation and confusion and to investigate the relationship between trihexyphenidyl - induced subjective effects and objective memory performance .
### Output Text:
OBJECTIVES : The objectives of this study were to examine the relationship between APOE epsilon4 and subjective effects of <span class="chemical">trihexyphenidyl</span> on measures reflecting sedation and confusion and to investigate the relationship between <span class="chemical">trihexyphenidyl</span> - induced subjective effects and objective memory performance . 