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: Repeated doses of edrophonium to 70 mg and neostigmine to 2 . 5 mg did not antagonize or augment the block .
### Output Text:
Repeated doses of <span class="chemical">edrophonium</span> to 70 mg and <span class="chemical">neostigmine</span> to 2 . 5 mg did not antagonize or augment the block . 