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: Compared to amiloride treatment , the chlorthalidone phase was associated with an increased frequency of ventricular ectopic beats ( 24 - hour Holter monitoring ) and a higher Lown grading , increased upslope and duration of the monophasic action potential , prolonged ventricular effective refractory period , and increased electrical instability during programmed ventricular stimulation .
### Output Text:
Compared to <span class="chemical">amiloride</span> treatment , the <span class="chemical">chlorthalidone</span> phase was associated with an increased frequency of ventricular ectopic beats ( 24 - hour Holter monitoring ) and a higher Lown grading , increased upslope and duration of the monophasic action potential , prolonged ventricular effective refractory period , and increased electrical instability during programmed ventricular stimulation . 