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: Contemporary experiences indicate that reduced doses are also needed in patients with conditions associated with hepatic hypoperfusion , e . g . heart failure , yet are unnecessary for renal dysfunction , adult age , sex , race / ethnicity or obesity .
### Output Text:
Contemporary experiences indicate that reduced doses are also needed in patients with conditions associated with hepatic hypoperfusion , e . g . heart failure , yet are unnecessary for renal dysfunction , adult age , sex , race / ethnicity or obesity . 