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: On the other hand , the pressor response to i . c . carbachol ( 1 mug ) was almost completely blocked by i . c . atropine ( 3 mug ) or hexamethonium ( 500 mug ) , and significantly reduced by i . c . chlorpromazine ( 50 mug ) but significantly potentiated by i . c . desmethylimipramine ( 30 mug ) .
### Output Text:
On the other hand , the pressor response to i . c . <span class="chemical">carbachol</span> ( 1 mug ) was almost completely blocked by i . c . <span class="chemical">atropine</span> ( 3 mug ) or <span class="chemical">hexamethonium</span> ( 500 mug ) , and significantly reduced by i . c . <span class="chemical">chlorpromazine</span> ( 50 mug ) but significantly potentiated by i . c . <span class="chemical">desmethylimipramine</span> ( 30 mug ) . 