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: Clinicians should increase their awareness for potential complication of valproate , especially in transplanted patients .
### Output Text:
Clinicians should increase their awareness for potential complication of <span class="chemical">valproate</span> , especially in transplanted patients . 