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: Male Sprague - Dawley rats were treated with D - penicillamine ( D - pen ) 500 mg / kg / day for 10 or 42 days .
### Output Text:
Male Sprague - Dawley rats were treated with <span class="chemical">D - penicillamine</span> ( <span class="chemical">D - pen</span> ) 500 mg / kg / day for 10 or 42 days . 