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: This report documents the unusual occurrence of rapidly progressive glomerulonephritis with crescents and fibrillar glomerulonephritis in a patient treated with rifampin .
### Output Text:
This report documents the unusual occurrence of rapidly progressive glomerulonephritis with crescents and fibrillar glomerulonephritis in a patient treated with <span class="chemical">rifampin</span> . 