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 carbamazepine was discontinued , two of the children returned to their former state very quickly , two had the minor motor seizures resolve in 3 and 6 months , and one had the seizures persist .
### Output Text:
When the <span class="chemical">carbamazepine</span> was discontinued , two of the children returned to their former state very quickly , two had the minor motor seizures resolve in 3 and 6 months , and one had the seizures persist . 