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: BACKGROUND : While the incidence of new - onset diabetes mellitus may be increasing in patients with schizophrenia treated with certain atypical antipsychotic agents , it remains unclear whether atypical agents are directly affecting glucose metabolism or simply increasing known risk factors for diabetes .
### Output Text:
BACKGROUND : While the incidence of new - onset diabetes mellitus may be increasing in patients with schizophrenia treated with certain atypical antipsychotic agents , it remains unclear whether atypical agents are directly affecting <span class="chemical">glucose</span> metabolism or simply increasing known risk factors for diabetes . 