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: Myocardial hypertrophy completely resolved upon reducing the target concentration of tacrolimus and did not recur , as confirmed at echocardiography and myocardial biopsy .
### Output Text:
Myocardial hypertrophy completely resolved upon reducing the target concentration of <span class="chemical">tacrolimus</span> and did not recur , as confirmed at echocardiography and myocardial biopsy . 