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: The incidence of ischemic episodes per patient per hour was 0 . 05 + / - 0 . 02 prior to 5 - FU infusion v 0 . 13 + / - 0 . 03 during 5 - FU infusion ( P less than . 001 ) ; the duration of ECG changes was 0 . 6 + / - 0 . 3 minutes per patient per hour before 5 - FU v 1 . 9 + / - 0 . 5 minutes per patient per hour during 5 - FU ( P less than . 01 ) .
### Output Text:
The incidence of ischemic episodes per patient per hour was 0 . 05 + / - 0 . 02 prior to <span class="chemical">5 - FU</span> infusion v 0 . 13 + / - 0 . 03 during <span class="chemical">5 - FU</span> infusion ( P less than . 001 ) ; the duration of ECG changes was 0 . 6 + / - 0 . 3 minutes per patient per hour before <span class="chemical">5 - FU</span> v 1 . 9 + / - 0 . 5 minutes per patient per hour during <span class="chemical">5 - FU</span> ( P less than . 01 ) . 