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: Severe side effects in terms of mental confusion and progressive hyperbilirubinemia , however , point to an enhancement not only of antineoplastic effects but also of toxicity in normal tissues .
### Output Text:
Severe side effects in terms of mental confusion and progressive hyperbilirubinemia , however , point to an enhancement not only of antineoplastic effects but also of toxicity in normal tissues . 