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: When deferoxamine therapy was discontinued and serial studies were performed , audiograms in seven cases reverted to normal or near normal within two to three weeks , and nine of 13 patients with symptoms became asymptomatic .
### Output Text:
When <span class="chemical">deferoxamine</span> therapy was discontinued and serial studies were performed , audiograms in seven cases reverted to normal or near normal within two to three weeks , and nine of 13 patients with symptoms became asymptomatic . 