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: A positive lymphocyte transformation test with indomethacin in vitro further substantiates the potential role of this drug in causing aplastic anemia in a susceptible patient .
### Output Text:
A positive lymphocyte transformation test with <span class="chemical">indomethacin</span> in vitro further substantiates the potential role of this drug in causing aplastic anemia in a susceptible patient . 