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: Levetiracetam as an adjunct to phenobarbital treatment in cats with suspected idiopathic epilepsy .
### Output Text:
<span class="chemical">Levetiracetam</span> as an adjunct to <span class="chemical">phenobarbital</span> treatment in cats with suspected idiopathic epilepsy . 