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 four patients , polymorphous ventricular tachycardia appeared after intravenous administration of 200 to 400 mg of procainamide for the treatment of sustained ventricular tachycardia .
### Output Text:
In four patients , polymorphous ventricular tachycardia appeared after intravenous administration of 200 to 400 mg of <span class="chemical">procainamide</span> for the treatment of sustained ventricular tachycardia . 