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: We recorded indication for conversion , whether conversion was early or late after transplantation , tacrolimus dose and trough blood level at conversion , and incidence of rejection after conversion .
### Output Text:
We recorded indication for conversion , whether conversion was early or late after transplantation , <span class="chemical">tacrolimus</span> dose and trough blood level at conversion , and incidence of rejection after conversion . 