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: CONCLUSIONS : Our observations suggest that the spectrum of rosaceiform dermatitis as a complication of treatment with tacrolimus ointment is heterogeneous .
### Output Text:
CONCLUSIONS : Our observations suggest that the spectrum of rosaceiform dermatitis as a complication of treatment with <span class="chemical">tacrolimus</span> ointment is heterogeneous . 