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: Based on these observations , it is concluded that 5 - HT2 blockade obtained with risperidone at D2 occupancy rates of 60 % and above does not appear to protect against the risk for extrapyramidal side effects .
### Output Text:
Based on these observations , it is concluded that 5 - HT2 blockade obtained with <span class="chemical">risperidone</span> at D2 occupancy rates of 60 % and above does not appear to protect against the risk for extrapyramidal side effects . 