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: When the metoclopramide administration was discontinued , the abnormal movements gradually improved to a considerable extent .
### Output Text:
When the <span class="chemical">metoclopramide</span> administration was discontinued , the abnormal movements gradually improved to a considerable extent . 