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: We conclude that 5 - FU infusion is associated with a significant increase in silent ST segment deviation suggestive of ischemia , particularly among patients with coronary artery disease .
### Output Text:
We conclude that <span class="chemical">5 - FU</span> infusion is associated with a significant increase in silent ST segment deviation suggestive of ischemia , particularly among patients with coronary artery disease . 