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 dosage of indocyanine green used for angiography varied from 25 to 75 mg , depending upon the institution .
### Output Text:
The dosage of <span class="chemical">indocyanine green</span> used for angiography varied from 25 to 75 mg , depending upon the institution . 