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: Prophylactic administration of lamivudine in patients who required immunosuppressive therapy seems to be safe , well tolerated and effective in preventing HBV reactivation .
### Output Text:
Prophylactic administration of <span class="chemical">lamivudine</span> in patients who required immunosuppressive therapy seems to be safe , well tolerated and effective in preventing HBV reactivation . 