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 risk of VNR cardiac events was similar to vindesine ( VDS ) and other cardiotoxic drugs [ fluorouracil , anthracyclines , gemcitabine ( GEM ) em leader ] .
### Output Text:
The risk of <span class="chemical">VNR</span> cardiac events was similar to <span class="chemical">vindesine</span> ( <span class="chemical">VDS</span> ) and other cardiotoxic drugs [ <span class="chemical">fluorouracil</span> , <span class="chemical">anthracyclines</span> , <span class="chemical">gemcitabine</span> ( <span class="chemical">GEM</span> ) em leader ] . 