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: There was no indication that sertraline exacerbated the impairment produced by haloperidol since an equivalent effect also occurred in the placebo group .
### Output Text:
There was no indication that <span class="chemical">sertraline</span> exacerbated the impairment produced by <span class="chemical">haloperidol</span> since an equivalent effect also occurred in the placebo group . 