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 case of fatal aplastic anemia is described in which no drugs other than allopurinol and indomethacin were given .
### Output Text:
A case of fatal aplastic anemia is described in which no drugs other than <span class="chemical">allopurinol</span> and <span class="chemical">indomethacin</span> were given . 