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: High doses of atropine ( up to 50 mg per 24 hours ) , adrenaline and dopamine were necessary .
### Output Text:
High doses of <span class="chemical">atropine</span> ( up to 50 mg per 24 hours ) , <span class="chemical">adrenaline</span> and <span class="chemical">dopamine</span> were necessary . 