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: Appropriate treatment consists of discontinuation of heparin , and anticoagulation with sodium warfarin if necessary .
### Output Text:
Appropriate treatment consists of discontinuation of <span class="chemical">heparin</span> , and anticoagulation with <span class="chemical">sodium warfarin</span> if necessary . 