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: The safety and efficacy of total dose infusion ( TDI ) of iron dextran has been well documented .
### Output Text:
The safety and efficacy of total dose infusion ( TDI ) of <span class="chemical">iron dextran</span> has been well documented . 