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: Allopregnanolone and pregnanolone , but not ganaxolone , also reduced cumulative lethality associated with kindling .
### Output Text:
<span class="chemical">Allopregnanolone</span> and <span class="chemical">pregnanolone</span> , but not <span class="chemical">ganaxolone</span> , also reduced cumulative lethality associated with kindling . 