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: Considering that clozapine remains the gold standard in treatment of resistant psychosis , there is an urgent need to raise awareness among medical and paramedical staff involved in the care of these patients .
### Output Text:
Considering that <span class="chemical">clozapine</span> remains the gold standard in treatment of resistant psychosis , there is an urgent need to raise awareness among medical and paramedical staff involved in the care of these patients . 