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: After delivery of the infant , there should be no contraindication to the use of an alpha - adrenergic vasopressor such as phenylephrine to treat hypotensive patients with tachycardia .
### Output Text:
After delivery of the infant , there should be no contraindication to the use of an alpha - adrenergic vasopressor such as <span class="chemical">phenylephrine</span> to treat hypotensive patients with tachycardia . 