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: After 5 weeks of bupropion use , the subject experienced a generalized tonic clonic seizure after staying up nearly all night packing and moving to a new residence .
### Output Text:
After 5 weeks of <span class="chemical">bupropion</span> use , the subject experienced a generalized tonic clonic seizure after staying up nearly all night packing and moving to a new residence . 