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: Since 1989 , she had been suffering from systemic lupus erythematosus ( SLE ) with renal involvement and undergone periods of treatment with azathioprine and cyclophosphamide .
### Output Text:
Since 1989 , she had been suffering from systemic lupus erythematosus ( SLE ) with renal involvement and undergone periods of treatment with <span class="chemical">azathioprine</span> and <span class="chemical">cyclophosphamide</span> . 