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: After pretreatment with 3 mg of cyproheptadine , 2 mg mianserin , or 2 mg chlorpheniramine , only 5 of 105 animals ( 5 % ) died after receiving BSA on day + 7 ( p less than 0 . 001 ) .
### Output Text:
After pretreatment with 3 mg of <span class="chemical">cyproheptadine</span> , 2 mg <span class="chemical">mianserin</span> , or 2 mg <span class="chemical">chlorpheniramine</span> , only 5 of 105 animals ( 5 % ) died after receiving BSA on day + 7 ( p less than 0 . 001 ) . 