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: Patients likely to have both raised trough - concentrations and mental confusion are those with both severe renal and hepatic dysfunction .
### Output Text:
Patients likely to have both raised trough - concentrations and mental confusion are those with both severe renal and hepatic dysfunction . 