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: CCNU was administered per os ( PO ) at a targeted dosage of 60 mg / m ( 2 ) body surface area on day 0 , CTX was administered PO at a targeted dosage of 250 mg / m ( 2 ) divided over days 0 through 4 , and all dogs received prophylactic antibiotics .
### Output Text:
<span class="chemical">CCNU</span> was administered per os ( PO ) at a targeted dosage of 60 mg / m ( 2 ) body surface area on day 0 , <span class="chemical">CTX</span> was administered PO at a targeted dosage of 250 mg / m ( 2 ) divided over days 0 through 4 , and all dogs received prophylactic antibiotics . 