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: Hypertension in diabetics prone to hypoglycaemia attacks should not be treated with beta - blockers because these drugs may cause a sharp rise in blood - pressure in such patients .
### Output Text:
Hypertension in diabetics prone to hypoglycaemia attacks should not be treated with beta - blockers because these drugs may cause a sharp rise in blood - pressure in such patients . 