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: An analysis of the 75 cases that had been adequately followed up suggested that 16 , including three deaths , were probably related to treatment with the drug .
### Output Text:
An analysis of the 75 cases that had been adequately followed up suggested that 16 , including three deaths , were probably related to treatment with the drug . 