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 hypotensive effect of 100 mg / kg alpha - methyldopa was also partially reversed by naloxone .
### Output Text:
The hypotensive effect of 100 mg / kg <span class="chemical">alpha - methyldopa</span> was also partially reversed by <span class="chemical">naloxone</span> . 