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: The objective of this study was to determine whether ephedrine , an alpha - and beta - adrenergic agonist previously shown to enhance genital blood flow in women , has beneficial effects in reversing antidepressant - induced sexual dysfunction .
### Output Text:
The objective of this study was to determine whether <span class="chemical">ephedrine</span> , an alpha - and beta - adrenergic agonist previously shown to enhance genital blood flow in women , has beneficial effects in reversing antidepressant - induced sexual dysfunction . 