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: Patients aged 18 years or older treated with prochlorperazine for headache , nausea , or vomiting were eligible for inclusion .
### Output Text:
Patients aged 18 years or older treated with <span class="chemical">prochlorperazine</span> for headache , nausea , or vomiting were eligible for inclusion . 