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: Orthostatic hypotension was ameliorated 4 days after withdrawal of selegiline and totally abolished 7 days after discontinuation of the drug .
### Output Text:
Orthostatic hypotension was ameliorated 4 days after withdrawal of <span class="chemical">selegiline</span> and totally abolished 7 days after discontinuation of the drug . 