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: Patients taking clozapine and olanzapine must be examined for insulin resistance and its consequences .
### Output Text:
Patients taking <span class="chemical">clozapine</span> and <span class="chemical">olanzapine</span> must be examined for insulin resistance and its consequences . 