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: Thus , myocardial electrical excitability was measured in patients with mild essential hypertension and known coronary artery disease after 8 weeks of treatment with a potassium - conserving diuretic ( amiloride ) and a similar period on a potassium - losing diuretic ( chlorthalidone ) in a randomised study .
### Output Text:
Thus , myocardial electrical excitability was measured in patients with mild essential hypertension and known coronary artery disease after 8 weeks of treatment with a <span class="chemical">potassium</span> - conserving diuretic ( <span class="chemical">amiloride</span> ) and a similar period on a <span class="chemical">potassium</span> - losing diuretic ( <span class="chemical">chlorthalidone</span> ) in a randomised study . 