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: The above results indicate that because potassium - losing diuretic therapy can increase myocardial electrical excitability in patients with ischaemic heart disease , even minor falls in plasma potassium concentrations are probably best avoided in such patients .
### Output Text:
The above results indicate that because <span class="chemical">potassium</span> - losing diuretic therapy can increase myocardial electrical excitability in patients with ischaemic heart disease , even minor falls in plasma <span class="chemical">potassium</span> concentrations are probably best avoided in such patients . 