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: The patient had been treated with tiapride or tetrabenazine alone without any adverse effects before the administration of the combination therapy .
### Output Text:
The patient had been treated with <span class="chemical">tiapride</span> or <span class="chemical">tetrabenazine</span> alone without any adverse effects before the administration of the combination therapy . 