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: RESULTS : A 20 - year - old male with schizophrenia developed a sudden onset of myocarditis after commencement of clozapine .
### Output Text:
RESULTS : A 20 - year - old male with schizophrenia developed a sudden onset of myocarditis after commencement of <span class="chemical">clozapine</span> . 