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: This case highlights that drug - induced blood dyscrasias can occur unexpectedly as a result of treatment with a commonly used drug thought to be " safe " .
### Output Text:
This case highlights that drug - induced blood dyscrasias can occur unexpectedly as a result of treatment with a commonly used drug thought to be " safe " . 