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: Hepatitis may develop weeks after discontinuation of the drug and may run a prolonged course , but complete remission was observed in all reported cases .
### Output Text:
Hepatitis may develop weeks after discontinuation of the drug and may run a prolonged course , but complete remission was observed in all reported cases . 