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: RESULTS : Switches to hypomania or mania occurred in 27 % of all patients ( N = 12 ) ( and in 24 % of the subgroup of patients treated with SSRIs [ 8 / 33 ] ) ; 16 % ( N = 7 ) experienced manic episodes , and 11 % ( N = 5 ) experienced hypomanic episodes .
### Output Text:
RESULTS : Switches to hypomania or mania occurred in 27 % of all patients ( N = 12 ) ( and in 24 % of the subgroup of patients treated with <span class="chemical">SSRIs</span> [ 8 / 33 ] ) ; 16 % ( N = 7 ) experienced manic episodes , and 11 % ( N = 5 ) experienced hypomanic episodes . 