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: Two schizophrenic patients , who had a prior history of LSD abuse and who had previously developed EPS with classic antipsychotics , were successfully treated with risperidone .
### Output Text:
Two schizophrenic patients , who had a prior history of <span class="chemical">LSD</span> abuse and who had previously developed EPS with classic antipsychotics , were successfully treated with <span class="chemical">risperidone</span> . 