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: Controlling for relevant covariates , we also found treatment with selective serotonin reuptake inhibitors ( SSRIs ) to be associated with lower trabecular BMD at the radius ( P = . 03 ) and BMD z score at the lumbar spine ( P < . 05 ) .
### Output Text:
Controlling for relevant covariates , we also found treatment with selective <span class="chemical">serotonin</span> reuptake inhibitors ( SSRIs ) to be associated with lower trabecular BMD at the radius ( P = . 03 ) and BMD z score at the lumbar spine ( P < . 05 ) . 