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: Associated factors were co - treatment with other centrally antimuscarinic agents , poor clinical outcome , older age , and longer hospitalization ( by 17 . 5 days , increasing cost ) ; sex , diagnosis or medical co - morbidity , and daily clozapine dose , which fell with age , were unrelated .
### Output Text:
Associated factors were co - treatment with other centrally antimuscarinic agents , poor clinical outcome , older age , and longer hospitalization ( by 17 . 5 days , increasing cost ) ; sex , diagnosis or medical co - morbidity , and daily <span class="chemical">clozapine</span> dose , which fell with age , were unrelated . 