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: Optimal control of the absences was achieved with sodium valproate , lamotrigine , or ethosuximide alone or in combination .
### Output Text:
Optimal control of the absences was achieved with <span class="chemical">sodium valproate</span> , <span class="chemical">lamotrigine</span> , or <span class="chemical">ethosuximide</span> alone or in combination . 