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: DISCUSSION : To our knowledge , this is the first reported case of venlafaxine overdose that resulted in a generalized seizure .
### Output Text:
DISCUSSION : To our knowledge , this is the first reported case of <span class="chemical">venlafaxine</span> overdose that resulted in a generalized seizure . 