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: Clinicians should be alert to the possibility of hyperkalemia , especially in elderly patients using ACE / ARB in combination with potassium sparing agents and who have mild renal disturbance .
### Output Text:
Clinicians should be alert to the possibility of hyperkalemia , especially in elderly patients using ACE / ARB in combination with <span class="chemical">potassium</span> sparing agents and who have mild renal disturbance . 