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: Immune hemolytic anemia due to a drug - adsorption mechanism has been described primarily in patients receiving penicillins and first - generation cephalosporins .
### Output Text:
Immune hemolytic anemia due to a drug - adsorption mechanism has been described primarily in patients receiving <span class="chemical">penicillins</span> and first - generation <span class="chemical">cephalosporins</span> . 