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: In the remaining three patients , procainamide was administered orally for treatment of chronic premature ventricular contractions or atrial flutter .
### Output Text:
In the remaining three patients , <span class="chemical">procainamide</span> was administered orally for treatment of chronic premature ventricular contractions or atrial flutter . 