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: However , the torsadogenic potential of metoclopramide , a commonly used antiemetic and prokinetic drug , has not been reported in the literature , despite its chemical similarity to procainamide .
### Output Text:
However , the torsadogenic potential of <span class="chemical">metoclopramide</span> , a commonly used antiemetic and prokinetic drug , has not been reported in the literature , despite its chemical similarity to <span class="chemical">procainamide</span> . 