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: Acetaminophen ( APAP ) produces proximal tubular necrosis in Fischer 344 ( F344 ) rats .
### Output Text:
<span class="chemical">Acetaminophen</span> ( <span class="chemical">APAP</span> ) produces proximal tubular necrosis in Fischer 344 ( F344 ) rats . 