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: Naloxone ( 0 . 3 , 1 , 3 , and 10 mg / kg ) injected prior to training attenuated the retention deficit with a peak of activity at 3 mg / kg .
### Output Text:
<span class="chemical">Naloxone</span> ( 0 . 3 , 1 , 3 , and 10 mg / kg ) injected prior to training attenuated the retention deficit with a peak of activity at 3 mg / kg . 