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: Thus , hyperammonemia is capable of altering drug action and must be considered along with impaired drug metabolism in enhanced drug responses associated with liver disease .
### Output Text:
Thus , hyperammonemia is capable of altering drug action and must be considered along with impaired drug metabolism in enhanced drug responses associated with liver disease . 