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: From Days 9 to 25 , subjects were randomly assigned to either sertraline ( 12 subjects ) or placebo ( 12 subjects ) ; the sertraline dose was titrated from 50 to 200 mg / day from Days 9 to 16 , and remained at 200 mg / day for the final 10 days of the drug administration period .
### Output Text:
From Days 9 to 25 , subjects were randomly assigned to either <span class="chemical">sertraline</span> ( 12 subjects ) or placebo ( 12 subjects ) ; the <span class="chemical">sertraline</span> dose was titrated from 50 to 200 mg / day from Days 9 to 16 , and remained at 200 mg / day for the final 10 days of the drug administration period . 