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 two patients , LTG exacerbated MJ in a delayed but more severe manner , with myoclonic status that only ceased after LTG withdrawal .
### Output Text:
In two patients , <span class="chemical">LTG</span> exacerbated MJ in a delayed but more severe manner , with myoclonic status that only ceased after <span class="chemical">LTG</span> withdrawal . 