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 ganglionic blocker trimethaphan ( 5 mg / kg i . v . ) caused similar reductions in mean arterial pressure in both lesioned and sham groups .
### Output Text:
The ganglionic blocker <span class="chemical">trimethaphan</span> ( 5 mg / kg i . v . ) caused similar reductions in mean arterial pressure in both lesioned and sham groups . 