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: BACKGROUND : Risperidone , a potent antagonist of both serotonergic ( 5HT2A ) and dopaminergic D2 receptors is associated with hyperprolactinemia in adults and children .
### Output Text:
BACKGROUND : <span class="chemical">Risperidone</span> , a potent antagonist of both serotonergic ( 5HT2A ) and dopaminergic D2 receptors is associated with hyperprolactinemia in adults and children . 