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: Visual and auditory neurotoxicity was previously documented in 42 of 89 patients with transfusion - dependent anemia who were receiving iron chelation therapy with daily subcutaneous deferoxamine .
### Output Text:
Visual and auditory neurotoxicity was previously documented in 42 of 89 patients with transfusion - dependent anemia who were receiving <span class="chemical">iron</span> chelation therapy with daily subcutaneous <span class="chemical">deferoxamine</span> . 