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: Lamivudine therapy was started 3 - 7 days prior to immunosuppressive therapy in all patients .
### Output Text:
<span class="chemical">Lamivudine</span> therapy was started 3 - 7 days prior to immunosuppressive therapy in all patients . 