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: A nonregenerative anemia was the most compromising of the cytopenias and occurred in approximately 50 % of dogs receiving 400 - 500 mg / kg cefonicid or 540 - 840 mg / kg cefazedone .
### Output Text:
A nonregenerative anemia was the most compromising of the cytopenias and occurred in approximately 50 % of dogs receiving 400 - 500 mg / kg <span class="chemical">cefonicid</span> or 540 - 840 mg / kg <span class="chemical">cefazedone</span> . 