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 literature review suggests that general practitioners should prescribe scabicides with increased caution for certain at - risk groups , and give adequate warnings regarding potential toxicity .
### Output Text:
This literature review suggests that general practitioners should prescribe scabicides with increased caution for certain at - risk groups , and give adequate warnings regarding potential toxicity . 