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: CONCLUSION : A 50 % reduction in the incidence of akathisia when prochlorperazine was administered by means of 15 - minute intravenous infusion versus a 2 - minute intravenous push was not detected .
### Output Text:
CONCLUSION : A 50 % reduction in the incidence of akathisia when <span class="chemical">prochlorperazine</span> was administered by means of 15 - minute intravenous infusion versus a 2 - minute intravenous push was not detected . 