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 patient underwent a 10 - month regimen of rifampin and isoniazid for pulmonary tuberculosis and was discovered to have developed signs of severe renal failure five weeks after completion of therapy .
### Output Text:
This patient underwent a 10 - month regimen of <span class="chemical">rifampin</span> and <span class="chemical">isoniazid</span> for pulmonary tuberculosis and was discovered to have developed signs of severe renal failure five weeks after completion of therapy . 