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: Bpd was administered to 459 patients ( 361 males , 63 + / - 12 years old ) comprising 378 AF and 81 AFL cases .
### Output Text:
<span class="chemical">Bpd</span> was administered to 459 patients ( 361 males , 63 + / - 12 years old ) comprising 378 AF and 81 AFL cases . 