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: PATIENTS AND METHODS : A total of 77 chronic hepatitis B patients who had not been treated with lamivudine were included in the study .
### Output Text:
PATIENTS AND METHODS : A total of 77 chronic hepatitis B patients who had not been treated with <span class="chemical">lamivudine</span> were included in the study . 