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: A previously healthy child who developed acute , severe , rapidly progressive vanishing bile duct syndrome shortly after Stevens - Johnson syndrome is described ; this was temporally associated with ibuprofen use .
### Output Text:
A previously healthy child who developed acute , severe , rapidly progressive vanishing bile duct syndrome shortly after Stevens - Johnson syndrome is described ; this was temporally associated with <span class="chemical">ibuprofen</span> use . 