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: We report an investigation from a local surveillance for serious adverse drug reactions associated with disease modifying anti - rheumatic drugs that was triggered by the occurrence of liver failure in two of our patients .
### Output Text:
We report an investigation from a local surveillance for serious adverse drug reactions associated with disease modifying anti - rheumatic drugs that was triggered by the occurrence of liver failure in two of our patients . 