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: The risks of aprotinin and tranexamic acid in cardiac surgery : a one - year follow - up of 1188 consecutive patients .
### Output Text:
The risks of aprotinin and <span class="chemical">tranexamic acid</span> in cardiac surgery : a one - year follow - up of 1188 consecutive patients . 