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: To assess the antioxidant effects of atorvastatin ( atorva ) on dexamethasone ( dex ) - induced hypertension , 60 male Sprague - Dawley rats were treated with atorva 30 mg / kg / day or tap water for 15 days .
### Output Text:
To assess the antioxidant effects of <span class="chemical">atorvastatin</span> ( <span class="chemical">atorva</span> ) on <span class="chemical">dexamethasone</span> ( <span class="chemical">dex</span> ) - induced hypertension , 60 male Sprague - Dawley rats were treated with <span class="chemical">atorva</span> 30 mg / kg / day or tap water for 15 days . 