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: In the present paper the authors describe 2 female patients who developed incontinence secondary to the selective serotonin reuptake inhibitors paroxetine and sertraline , as well as a third who developed this side effect on venlafaxine .
### Output Text:
In the present paper the authors describe 2 female patients who developed incontinence secondary to the selective <span class="chemical">serotonin</span> reuptake inhibitors <span class="chemical">paroxetine</span> and <span class="chemical">sertraline</span> , as well as a third who developed this side effect on <span class="chemical">venlafaxine</span> . 