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: Iopentol and iohexol also produced significantly less decrease in aortic blood pressure than metrizoate at the different doses .
### Output Text:
<span class="chemical">Iopentol</span> and <span class="chemical">iohexol</span> also produced significantly less decrease in aortic blood pressure than <span class="chemical">metrizoate</span> at the different doses . 