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 18 of the 22 patients were initially receiving deferoxamine doses in excess of the commonly recommended 50 mg / kg per dose , therapy was restarted with lower doses , usually 50 mg / kg per dose or less depending on the degree of auditory abnormality , and with the exception of two cases no further toxicity was demonstrated .
### Output Text:
Since 18 of the 22 patients were initially receiving <span class="chemical">deferoxamine</span> doses in excess of the commonly recommended 50 mg / kg per dose , therapy was restarted with lower doses , usually 50 mg / kg per dose or less depending on the degree of auditory abnormality , and with the exception of two cases no further toxicity was demonstrated . 