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 this report we present four patients treated with a combination of different psychotropic drugs , in whom asterixis was triggered either by adding carbamazepine ( CBZ ) to a treatment regimen , or by increasing its dosage .
### Output Text:
In this report we present four patients treated with a combination of different psychotropic drugs , in whom asterixis was triggered either by adding <span class="chemical">carbamazepine</span> ( <span class="chemical">CBZ</span> ) to a treatment regimen , or by increasing its dosage . 