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: Rats were treated with a single IV injection of puromycin aminonucleoside , ( PAN , 7 . 5 mg / kg ) and 24 hour urine samples were obtained prior to sacrifice on days 3 , 5 , 7 , 10 , 17 , 27 , 41 ( N = 5 - 10 per group ) .
### Output Text:
Rats were treated with a single IV injection of <span class="chemical">puromycin aminonucleoside</span> , ( <span class="chemical">PAN</span> , 7 . 5 mg / kg ) and 24 hour urine samples were obtained prior to sacrifice on days 3 , 5 , 7 , 10 , 17 , 27 , 41 ( N = 5 - 10 per group ) . 