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: OBSERVATIONS : Six adult patients with inflammatory facial dermatoses were treated with tacrolimus ointment because of the ineffectiveness of standard treatments .
### Output Text:
OBSERVATIONS : Six adult patients with inflammatory facial dermatoses were treated with <span class="chemical">tacrolimus</span> ointment because of the ineffectiveness of standard treatments . 