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: MEASUREMENTS : Information regarding major bleeding episodes , strokes , and warfarin use was obtained from patients , relatives , primary physicians , and medical records .
### Output Text:
MEASUREMENTS : Information regarding major bleeding episodes , strokes , and <span class="chemical">warfarin</span> use was obtained from patients , relatives , primary physicians , and medical records . 