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: We studied the efficacy and safety of propranolol in the treatment of PPA - induced hypertension .
### Output Text:
We studied the efficacy and safety of <span class="chemical">propranolol</span> in the treatment of <span class="chemical">PPA</span> - induced hypertension . 