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: Pneumocystis pneumonia ( PCP ) , a common opportunistic infection in HIV - infected individuals , is generally treated with high doses of co - trimoxazole .
### Output Text:
Pneumocystis pneumonia ( PCP ) , a common opportunistic infection in HIV - infected individuals , is generally treated with high doses of <span class="chemical">co - trimoxazole</span> . 