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: It was found that he was a poor metabolizer of all four drugs , indicating that their metabolism is under the same genetic control .
### Output Text:
It was found that he was a poor metabolizer of all four drugs , indicating that their metabolism is under the same genetic control . 