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: Ten patients and 12 pregnancies are reported where chronic propranolol has been administered .
### Output Text:
Ten patients and 12 pregnancies are reported where chronic <span class="chemical">propranolol</span> has been administered . 