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: To determine if routine risperidone treatment is associated with a unique degree of D2 receptor occupancy and pattern of clinical effects , we used [ 123I ] IBZM SPECT to determine D2 occupancy in subjects treated with routine clinical doses of risperidone ( n = 12 ) or haloperidol ( n = 7 ) .
### Output Text:
To determine if routine <span class="chemical">risperidone</span> treatment is associated with a unique degree of D2 receptor occupancy and pattern of clinical effects , we used [ 123I ] IBZM SPECT to determine D2 occupancy in subjects treated with routine clinical doses of <span class="chemical">risperidone</span> ( n = 12 ) or <span class="chemical">haloperidol</span> ( n = 7 ) . 