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: Such a temporal relationship between the use of mirtazapine and the symptoms of RLS in our patient did not support a potentiating effect of domperione on mirtazapine - associated RLS .
### Output Text:
Such a temporal relationship between the use of <span class="chemical">mirtazapine</span> and the symptoms of RLS in our patient did not support a potentiating effect of <span class="chemical">domperione</span> on <span class="chemical">mirtazapine</span> - associated RLS . 