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: Intravenous administration of prochlorperazine by 15 - minute infusion versus 2 - minute bolus does not affect the incidence of akathisia : a prospective , randomized , controlled trial .
### Output Text:
Intravenous administration of <span class="chemical">prochlorperazine</span> by 15 - minute infusion versus 2 - minute bolus does not affect the incidence of akathisia : a prospective , randomized , controlled trial . 