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 who received enalapril experienced clinically and statistically significantly less symptomatic hypotension ( 5 . 2 % ) than the patients who received prazosin ( 12 . 9 % ) .
### Output Text:
Patients who received <span class="chemical">enalapril</span> experienced clinically and statistically significantly less symptomatic hypotension ( 5 . 2 % ) than the patients who received <span class="chemical">prazosin</span> ( 12 . 9 % ) . 