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: METHODS : Verapamil 80 mg , p . o . was administered , and then PRL levels were measured at 8th and 16th hours , by immunometric chemiluminescence .
### Output Text:
METHODS : <span class="chemical">Verapamil</span> 80 mg , p . o . was administered , and then PRL levels were measured at 8th and 16th hours , by immunometric chemiluminescence . 