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: Totals of 128 cases and 650 controls were analysed for repeat use and 135 cases and 622 controls for switching patterns .
### Output Text:
Totals of 128 cases and 650 controls were analysed for repeat use and 135 cases and 622 controls for switching patterns . 