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: One patient group developed sinus tachycardias in the setting of a massive carbamazepine overdose .
### Output Text:
One patient group developed sinus tachycardias in the setting of a massive <span class="chemical">carbamazepine</span> overdose . 