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: It is important to understand the pharmacokinetics of medications in face of chronic renal failure , the possibility of drug interactions , and how these factors should help guide medication therapy in the ESRD patient .
### Output Text:
It is important to understand the pharmacokinetics of medications in face of chronic renal failure , the possibility of drug interactions , and how these factors should help guide medication therapy in the ESRD patient . 