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 seventh patient , a permanent ventricular pacemaker was inserted and , despite continuation of procainamide therapy , polymorphous ventricular tachycardia did not reoccur .
### Output Text:
In the seventh patient , a permanent ventricular pacemaker was inserted and , despite continuation of <span class="chemical">procainamide</span> therapy , polymorphous ventricular tachycardia did not reoccur . 