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: However , asymptomatic ST changes ( greater than or equal to 1 mm ST deviation ) were common : six of 25 patients ( 24 % ) had ST changes before 5 - FU infusion v 17 ( 68 % ) during 5 - FU infusion ( P less than . 002 ) .
### Output Text:
However , asymptomatic ST changes ( greater than or equal to 1 mm ST deviation ) were common : six of 25 patients ( 24 % ) had ST changes before <span class="chemical">5 - FU</span> infusion v 17 ( 68 % ) during <span class="chemical">5 - FU</span> infusion ( P less than . 002 ) . 