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: Following phenytoin administration , the patient developed acute severe bradycardia , refractory to atropine and adrenaline .
### Output Text:
Following <span class="chemical">phenytoin</span> administration , the patient developed acute severe bradycardia , refractory to <span class="chemical">atropine</span> and <span class="chemical">adrenaline</span> . 