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: Our results suggest that addition of phenylephrine to nitroglycerin is not beneficial in the treatment of patients with acute myocardial infarction .
### Output Text:
Our results suggest that addition of <span class="chemical">phenylephrine</span> to <span class="chemical">nitroglycerin</span> is not beneficial in the treatment of patients with acute myocardial infarction . 