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 three patients , LTG exacerbated MJ in a dose - dependent manner with early aggravation during titration .
### Output Text:
In three patients , <span class="chemical">LTG</span> exacerbated MJ in a dose - dependent manner with early aggravation during titration . 