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: Nasal hypoplasia with or without stippled epiphyses has now been reported in 11 infants born to mothers treated with warfarin during the first trimester , and a causal association is probable .
### Output Text:
Nasal hypoplasia with or without stippled epiphyses has now been reported in 11 infants born to mothers treated with <span class="chemical">warfarin</span> during the first trimester , and a causal association is probable . 