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: In conclusion , a 4 - week course of lamivudine was safe and effective in suppression of HBV DNA in Chinese HBsAg carriers .
### Output Text:
In conclusion , a 4 - week course of <span class="chemical">lamivudine</span> was safe and effective in suppression of HBV DNA in Chinese <span class="chemical">HBsAg</span> carriers . 