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: These data suggest a protective role for the central dopamine blocker haloperidol against death from high - dose amphetamine exposure without reducing the incidence of seizures .
### Output Text:
These data suggest a protective role for the central <span class="chemical">dopamine</span> blocker <span class="chemical">haloperidol</span> against death from high - dose <span class="chemical">amphetamine</span> exposure without reducing the incidence of seizures . 