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: This response was significantly reduced by the intravenous ( i . v . ) injection of guanethidine ( 5 mg ) , hexamethonium ( 10 mg ) or phentolamine ( 5 mg ) , and conversely , potentiated by i . v . desmethylimipramine ( 0 . 3 mg ) , while propranolol ( 0 . 5 mg ) i . v . selectively inhibited the enlargement of pulse pressure and the tachycardia following i . c . carbachol ( 1 mug ) .
### Output Text:
This response was significantly reduced by the intravenous ( i . v . ) injection of <span class="chemical">guanethidine</span> ( 5 mg ) , <span class="chemical">hexamethonium</span> ( 10 mg ) or <span class="chemical">phentolamine</span> ( 5 mg ) , and conversely , potentiated by i . v . <span class="chemical">desmethylimipramine</span> ( 0 . 3 mg ) , while <span class="chemical">propranolol</span> ( 0 . 5 mg ) i . v . selectively inhibited the enlargement of pulse pressure and the tachycardia following i . c . <span class="chemical">carbachol</span> ( 1 mug ) . 