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: A frequently fatal , although exceptionally rare side effect of carbamazepine is necrotizing eosinophilic ( hypersensitivity ) myocarditis .
### Output Text:
A frequently fatal , although exceptionally rare side effect of <span class="chemical">carbamazepine</span> is necrotizing eosinophilic ( hypersensitivity ) myocarditis . 