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: These events were temporally coincident with the initial use of high - dose tranexamic acid ( TXA ) therapy after withdrawal of aprotinin from general clinical usage .
### Output Text:
These events were temporally coincident with the initial use of high - dose <span class="chemical">tranexamic acid</span> ( <span class="chemical">TXA</span> ) therapy after withdrawal of aprotinin from general clinical usage . 