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: 5 patients with acute renal failure ( 3 with thrombopenia and hemolysis ) induced by the reintroduction of rifampicin are described .
### Output Text:
5 patients with acute renal failure ( 3 with thrombopenia and hemolysis ) induced by the reintroduction of <span class="chemical">rifampicin</span> are described . 