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 the prophylactic lamivudine group severe hepatitis were observed only in 1 patient ( 2 . 7 % ) of 37 patients ( p < 0 . 006 ) .
### Output Text:
In the prophylactic <span class="chemical">lamivudine</span> group severe hepatitis were observed only in 1 patient ( 2 . 7 % ) of 37 patients ( p < 0 . 006 ) . 