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: After the addition of clonidine 0 . 15 mg bid she developed complete AV block , which resolved after all therapy was stopped .
### Output Text:
After the addition of <span class="chemical">clonidine</span> 0 . 15 mg bid she developed complete AV block , which resolved after all therapy was stopped . 