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: CONCLUSIONS : Correlation of plasma argatroban concentration versus the patient ' s coagulation variables and clinical course suggest that prolonged elevated levels of plasma argatroban may have contributed to the patient ' s extended coagulopathy .
### Output Text:
CONCLUSIONS : Correlation of plasma <span class="chemical">argatroban</span> concentration versus the patient ' s coagulation variables and clinical course suggest that prolonged elevated levels of plasma <span class="chemical">argatroban</span> may have contributed to the patient ' s extended coagulopathy . 