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: Severe and long lasting cholestasis after high - dose co - trimoxazole treatment for Pneumocystis pneumonia in HIV - infected patients - - a report of two cases .
### Output Text:
Severe and long lasting cholestasis after high - dose <span class="chemical">co - trimoxazole</span> treatment for Pneumocystis pneumonia in HIV - infected patients - - a report of two cases . 