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 authors present a 10 - year - old boy chronically treated with lisinopril , an angiotensin converting enzyme inhibitor , to control hypertension who developed hypotension following the addition of tizanidine , an alpha - 2 agonist , for the treatment of spasticity .
### Output Text:
The authors present a 10 - year - old boy chronically treated with <span class="chemical">lisinopril</span> , an <span class="chemical">angiotensin</span> converting enzyme inhibitor , to control hypertension who developed hypotension following the addition of <span class="chemical">tizanidine</span> , an alpha - 2 agonist , for the treatment of spasticity . 