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: BACKGROUND : Nicotine polacrilex lozenges deliver 25 % to 27 % more nicotine compared with equivalent doses of nicotine polacrilex gum .
### Output Text:
BACKGROUND : <span class="chemical">Nicotine</span> polacrilex lozenges deliver 25 % to 27 % more <span class="chemical">nicotine</span> compared with equivalent doses of <span class="chemical">nicotine</span> polacrilex gum . 