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: From 1986 to 1998 , 29 cancer patients who had 32 episodes of transient hyperammonemic encephalopathy related to continuous infusion of 5 - fluorouracil ( 5 - FU ) were identified .
### Output Text:
From 1986 to 1998 , 29 cancer patients who had 32 episodes of transient hyperammonemic encephalopathy related to continuous infusion of <span class="chemical">5 - fluorouracil</span> ( <span class="chemical">5 - FU</span> ) were identified . 