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: As tranexamic acid is the only modifiable factor , its administration , particularly in doses exceeding 80 mg . kg ( - 1 ) , should be weighed against the risk of postoperative seizures .
### Output Text:
As <span class="chemical">tranexamic acid</span> is the only modifiable factor , its administration , particularly in doses exceeding 80 mg . kg ( - 1 ) , should be weighed against the risk of postoperative seizures . 