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: STUDY OBJECTIVE : We sought to compare the rate of akathisia after administration of intravenous prochlorperazine as a 2 - minute bolus or 15 - minute infusion .
### Output Text:
STUDY OBJECTIVE : We sought to compare the rate of akathisia after administration of intravenous <span class="chemical">prochlorperazine</span> as a 2 - minute bolus or 15 - minute infusion . 