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: Antithrombin ( 50 or 500 IU / kg / i . v . ) was administered to rats once a day for 10 days immediately after the injection of puromycin aminonucleoside ( 50 mg / kg / i . v . ) .
### Output Text:
Antithrombin ( 50 or 500 IU / kg / i . v . ) was administered to rats once a day for 10 days immediately after the injection of <span class="chemical">puromycin aminonucleoside</span> ( 50 mg / kg / i . v . ) . 