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: The compound P11 is introduced in doses of 0 . 25 and 0 . 50 mg / kg intravenously and 10 mg / kg orally .
### Output Text:
The compound <span class="chemical">P11</span> is introduced in doses of 0 . 25 and 0 . 50 mg / kg intravenously and 10 mg / kg orally . 